THE PATH OF DEGENERATION IN PLANTS 199 



that of other Cruciferse. If in the cauliflower the 

 arrested flowers corresponded to different ancestral 

 stages the case would be striking ; but this does 

 not occur. Primitively the flower contained only 

 the stamens and pistils, the essential organs of 

 reproduction. But we see that the cauliflower 

 produces first the anterior and posterior sepals 

 (fig. 69, A), then the lateral sepals (fig. 69, B), then 

 successively the petals (fig. 69, c), the four larger 

 stamens (fig. 69, D), and the two shorter stamens 

 (fig. 69, E). Moreover, the flowers display a special 

 readiness to the suppression of certain parts such 

 as the petals, as in the flower D (fig. 69). 



3. Progressive degeneration of the prothallus in 

 phanerogams. Although embryology gives us few 

 examples, morphology proves clearly enough that 

 in plant degeneration there is no return to ancestral 

 types. 



This appears clearly from a comparison of the 

 progressive evolution of the prothallus in crypto- 

 gams with its degeneration in phanerogams. 



Terrestrial vegetation has been derived entirely 

 from aquatic life. The Bryophyta (mosses and 

 liver-worts), the Vascular Cryptogams (ferns), and 

 the flowering plants all have sprung from aquatic 

 algae probably not very different from Coleochcete. 

 Such aquatic forms are reproduced by means of 

 true ova and spermatozoa. The terrestrial plants 

 which were derived from them had also spermatozoa 

 with vibratile locomotor hairs and impregnation 



