THE EVOLUTION OP PLANTS 127 



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 1 

 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 algae, preceded 

 more complex forms like 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. Qaz. 

 66: 185-228. Sept., 1918. 



