THE EVOLUTION OF PLANTS 1 27 



terpreted as reminiscent of an ancestral filamentous green 

 alga, and the appearance in the embryo of pines and 

 other conifers of a larger number of primordia than of 

 mature cotyledons, has also been regarded as a re- 

 capitulation of an ancestral feature (Fig. 104). Bucholz^ 

 has demonstrated that young pine embryos possess 

 an apical cell similar to that characteristic of ferns 

 and fern-allies, this apical cell persisting until the pine 

 embryo comprises several hundred cells, and then loosing 

 its identity (Fig. 64) . 



102. Evidence from Comparative Anatomy. — Compara- 

 tive study of structure has led to the conclusion that, 

 in its broadest aspects, the course of plant evolution has 

 been from the simple to the complex; that such simple 

 organisms as Pleurococcus, and other green algas, preceded 

 more complex forms Hke the liverworts; that Bryophytes 

 probably appeared before ferns, and they in turn before 

 the modern Gymnosperms and Angiosperms. 



A difficulty of accepting this conclusion as final is the 

 possibility that, at certain points, the course of evolution 

 may have been retrograde — i.e., from the more complex 

 to the less complex. For example, it is generally accepted 

 that the filamentous, alga-like fungi were derived from 

 green algae by retrograde evolution (degeneration). Were 

 the plants with one seed-leaf (monocotyledons) derived 

 from those with two (dicotyledons) by retrograde evolu- 

 tion, or were the dicotyledons derived from the monocoty- 

 ledons by progressive evolution? Evidence ascertained 

 by comparative studies of vascular anatomy and other de- 

 tails of structure points to the conclusion, that, although 



"Bucholz, J. T. Suspensor and Early Embryo of Pinus. Bot. Gas. 

 66: 185-228. Sept., 1918. 



