Is Dominated By Trachaeophytes Vascular Plants - Cells .

isdominated by Trachaeophytes, or "Vascular Plants".The success of this group is no doubt related to the factthat, in contrast to bryophytes, trachaeophytes posessxylem and phloem. As you remember from previouslectures and lab, xylem - the water conducting tissue contains tracheary elements - cells that are dead atmaturity with thick and lignified secondary cell walls.This tissue is very durable and makes excellent fossils! Asa result, we know much about how early tracheophyteslooked, and it is even is possible to trace the evolution ofincreased complexity in body form through time including the origin of leaves, roots, arborescence, andthe seed.This week, we will examine some of this fossil evidence aswell as current day representatives commonly called:The Pteridophytes - or "Non-Seed Plants" is theterm we apply to vascular plants with more-or-lessprimitive reproduction involving extensive multicellulargametophyte and sporophyte generations. In contrast tobryophytes, pteridophtyes have a dominantsporophyte (diploid) generation producing spores, anda reduced gametophyte generation - either free-livingor dependent on the sporophyte for nutrition. Manypteridophytes have a rhizome. In some, the rhizome ishighly branched and the plant forms dense permanentstands by vegetative propagation and colonialgrowth.The time in lab will be divided between looking at fossilevidence of ancient pteridophytes and analysis of theliving forms. You will also visit the Greenhouse to findadditional examples of different groups. For each groupin our survey, the following suggestions apply:Observe each group in turn.Consult your textbook and lecture notes for adescription of diagnostic features of both externalform and internal anatomy.Study the life cycles of each group. Be sure youunderstand how sexual reproduction works in eachcase.Using fresh or prepared material, observe anddraw what you see.Consult your textbook for useful descriptions,terminology, and pictures. A guide to material in thelab is provided by the links below:

You will also be preparing your own thin-sections of fossilPrimitive Pteridophytes & Psilophytamaterial, called peels. For instructions see:LycophytaSphenophytaPterophytadownload this lab in PDF format

Paleobotany, the study of ancient plants from fossils,has been very useful in our understanding of theevolutionary history and relationships of plants. Givenscant coverage of the topic in typical paleontologydocumentaries on TV (that focus almost exclusively ondinosaur or human bones) few people realize just howmuch detail about ancient plants and their ecology canbe recovered from fossils.Of course, recovering this information requires athorough knowledge of both external morphology andinternal anatomy of plants. Given your work so far inBotany, you are in a good position to see what you cando! In class, you will make acid etch peels of fossil plantmaterial to observe evidence of pteridophytes based ontheir anatomy.As a sourvenir of the course, the peels you makein class are yours to keep!As you know, plants cells produce cellulose cell wallsthat in the case of sclerenchyma can by quite robustand thick. During fossilization, many specimens aresquashed flat forming compressions. In other cases,specimens are permineralized - cell lumina becomefilled with sediment or crystalline precipitate entombingoriginal cell walls within solid three-dimensional rock.Over millions of years, volatile organic molecules arelost from the cell walls, and what remains is mostlyrefractory carbon much like the carbon in coal.However, because the carbon remains in the position ofthe original cell walls in permineralizations, one cansometimes find highly faithful replicas of the originaltissue. These can be interpreted from transverse andlongitudinal section just as one would analyze living planttissues.The trick, of course, is to make thesesections from solid rock!You will be working with material from two differentoccurrences in time:Lower Devonian plants representing members ofthe Trimerophyta (see text) - approximately 386million years old.Obtain a specimen cut into a block. Identify asurface with interesting plant material fromwhich you wish to make a peel.Gently polish the chosen surface on a glass plateusing # 600 carborundum abrasive powder.Rinse.In the sink, etch the surface using 5%

Plants, including extinct lycopsids, horsetails,ferns, and seed plants associated with coal seamsfrom the Carboniferous period - approximately310 million years old.In both cases, the plants have been permineralized withcalcium carbonate (limestone). The key here is thatcalcium carbonate is soluble in acid whereas refractorycarbon is not. Check with your TA for a demonstrationon how to prepare peels. The following are generalinstructions:hydrochloric acid for 30 sec. - 1 min.Thoroughly dry the surface without touching itusing a hair drier.Cut a sheet of cellulose acetate to an appropriatesize.Using acetone as solvent, lay the peel on thesurface. Try as best you can to avoid trapping airbubbles. Allow it to dry.When ready (check with your TA), remove thepeel from the rock. Immediately, cut off excessacetate and press the peel in a book for a fewminutes to make sure it stays flat.Observe under the dissection microscope. Seewhat plant parts you can identify! Ask your TAfor help.

Primitive vascular plants from the Devonian period werevery different from those of today! For the most part,sporophytes probably existed as colonial plants with anextensively branched rhizome and multiple uprightaerial shoots. The shoots were leafless although theymay have been ornamented with epidermalemergences such as trichomes, scales or spines. Theshoots of the sporophytes also bore sporangia,depending on the group, either terminally at the tip ofthe main shoot or branches, or laterally from the mainaxis.A progression of forms are observed in the fossil recordof Trachaeophytes starting in the Lower (early)Devonian with small equally dichotomous forms such asCooksonia. See the model of the plant at the right. By theUpper (late) Devonian, we see the origin of moderntree-sized forms about which you will hear more nextweek.In lab, you will look at some fossil examples from thisremarkable Devonian Period. The fossils come from theBinghamton University Paleobotanical Collection - one ofthe finest collections of Devonian plant fossils in NorthAmerica.Please be extra careful when handling thespecimens! They are delicate and very rare!You will also examine a modern pteridophyte, ofuncertain affinities, with features that are highly

reminiscent of early fossil tracheophytes - perhaps arelict from this early evolutionary radiation.For each group, observe and draw what you see.Evidence suggests that rhyniophytes - or plants verysimilar to them - were the ancestral group of all vascularplants. They appeared during the Silurian Period(439-408my) and died out during the Devonian Period(408-360my). Sporophytes, such as represented by thegenus Aglaophyton, had naked dichotomous brancheswith terminal sporangia, and a centrarch protostele.Gametophytes appear to have been very similar to thesporophytes in morphology, bearing gametangia interminal splash cups - much like some modernliverworts. The best evidence of both sporophytes andgametophytes are permineralized specimens from theRhynie Chert - a justly famous fossil locality inScotland.This group probably evolved from rhyniophytes duringthe Lower Devonian and may have been the ancestors ofmore evolved groups including modern ferns,horsetails, and seed plants. The sporophytes oftrimerophytes were significantly larger than that ofrhyniophytes and exhibited anisotomous branching.Typically there is a main axis with smaller lateralbranches some of which have clusters of terminalsporangia. Researchers believe that these side brancheswere the major photosynthetic organs of the plant andmay ultimately have evolved into leaves. Internally,Trimerophytes had a larger, sometimes lobed protostele.Gametophytes are unknown.This group, consisting of two modern genera Psilotumand Tmesipteris, is very strange indeed! Psilotum lacksroots or leaves but has an underground rhizome andphotosynthetic stems that dichotomously branch.Sporangia are born laterally on distal branches insynangia - fused clusters with typically three sporangia.It is possible that synangia represent lateral branches likethat seen in Trimerophytes that through evolution havebecome fused and highly reduced.Internally, the stems of Psilotum have an exarchprotostele. Gametophytes look like reduced sporophytesand are subterranean. Recent molecular evidencesuggests that the Psilophyta may be related to ferns.However, in overall form of the sporophyte, Psilotumserves as an excellent visual representation of what earlyvascular plants may have looked like. Take a small sample

of Psilotum and make a transverse section, Identify thethe vascular tissues and draw what you see. Also, lookfor synangia on stems of this plant. If you find them,open the sporangia and look for spores.LycophytaSphenophytaPterophyta

Non-fern pteridophytes are sometimes referred to as"fern allies". Although common today in someenvironments, fern allies have only moderate diversity.The fossil record makes it clear, however, that they weremuch more diverse in the past and the modern formsrepresent but a very incomplete sample! In the past,pteridophytes included arborescent species thatprobably served as principal canopy trees in manyancient environments. Pteridophytes were also morediverse reproductively in the past, including severalimportant forms with heterosporous reproduction producing sporangia with two different spore sizes thatgerminate to produce gametophytes of separate sexes.This extinct fossil group from the Lower Devonian isthought to be the ancestors of the Lycophyta.Sporophytes of the group were leafless anddichotomously branched like the rhyniophytes, andpossessed proximal branches that may have functionedas roots. Unlike the rhyniophytes, the zosterophylls hadkidney-shaped & homosporous sporangia bornelaterally on the main axis sometimes in strobili.Internally the group had an exarch protostele.