Bold • Development of Plants in Time 287 



attributes. Among these are similarity though this "record of rocks" is re- 

 in cellular organization, metabolism, markably long and uninterrupted in 

 reproductive phenomena (including such localities as the Grand Canyon, 

 sexuality, meiosis, and life cycles), in- there are few places where such a great 

 heritance, and the capacity for adapta- series of strata is exposed. Paleobota- 

 tion. The occurrence of the same nists are forced to rely on exposure of 

 active, photosvnchetic pigment, chloro- fossil-bearing strata by landslides, wash- 

 phyll a, throughout the plant kingdom outs, road and rail construction, and, 

 (except in fungi) and of the storage especially, by mining and drilling oper- 

 product, starch, in a great majority of ations. 



green plants, are examples of signifi- In spite of the incompleteness of 



cant, common attributes. The produc- the fossil record, considerable in- 



tion of archegonia, all consisting of formation has been obtained about 



venter and neck, however modified in plants of the past. Paleobotany has not 



liverworts, mosses, vascular crypto- shed direct light on the origin of life 



gams, cycads, and conifers is another itself, but indirect evidences of its exist- 



example of a widely distributed char- ence, such as calcareous (limestones) 



acteristic. In a word, there is a series of sediments and iron ores, are available 



attributes common to species, to in strata approximately IV2 billion 



genera, families, orders, classes, and, years old. The oldest organisms were 



finally, to divisions of plants— both aquatic, algal, fungal, and probably 



living and fossil— which indicate con- bacterial. Many calcareous (lime- 



tinuity. These are most satisfactorily encrusted) algae occurred in the lower 



explained on the basis of kinship. (Ordovician) strata of the Paleozoic. 



The fossil record presents us with The Silurian and Devonian strata of 



important information regarding the the Paleozoic are strikingly different 



course of evolution and the relation- from earlier ones in that they contain 



ship of various forms of plant life. As abundant remains of truly terrestrial 



the original, igneous rocks of the plants. Here are represented as fossils 



earth's crust weathered, particles were primitive precursors of all the vascular 



washed away and deposited as sedi- plants except the flowering plants, 



ments in bodies of water. Among these This gradual development of terrestrial 



particles, various organisms were de- plants with vascular tissues indicates a 



posited. Later, when compression correlation between the migration of 



transformed these mixed sediments plant life to land and the evolution of 



into rocks, the organic remains some- xylem and phloem. In spite of the rise 



times were preserved as fossils. These of the land plants, aquatic algae and 



are of various types and differ in the fungi have continued to flourish, ap- 



perfection of their preservation. The parently with little change, until the 



most perfectly preserved are petrifac- present. 



tions, in which details of microscopic Sedimentary rocks, of non-marine 

 structure are remarkably clear upon origin, of the late Paleozoic (Missis- 

 sectioning, sippian and Pennsylvanian) contain a 



The older strata of sedimentary wealth of fossils. An indirect evidence 



rocks obviously contain fossil remains of the abundance of photosynthetic 



of the most ancient organisms, while plants in the Pennsylvanian is the oc- 



strata deposited subsequently contain currence of extensive deposits of coal 



a series of increasingly more recent in that period. The Pennsylvanian 



organic remains, culminating in those often is called the "age of ferns" be- 



of extant (now living) plants. Al- cause of the abundance of fossilized 



