52 THEORY OF ORGANIC EVOLUTION. 



2. Asexual reproductive cells which arise by 

 budding, instead of separating, become cell branches 

 or branched cell threads. 



3. Reproductive cells which arise by free cell 

 formation become bodies which form a part of the 

 cell contents. 



4. Parts of a plant which arise by differentiation 

 lie side by side and form a body of web-like or 

 tissue-like structure. 



5. A definite and previously limited growth con- 

 tinues, or a definite formation of parts of an ontog- 

 eny which has previously been present but once, 

 is repeated. (Ampliation.) 



6. The parts of an ontogeny become dissimilar, 

 since the functions which were previously united 

 become differentiated and since new dissimilar 

 functions are produced in the various parts. This 

 differentiation is either one of space between the 

 parts of the ontogeny that appear near each other, or 

 one of time between those that are derived from 

 each other. 



7. Parts which have become dissimilar by differ- 

 entiation undergo a reduction, in which the inter- 

 mediate forms are suppressed and at last only the 

 qualitatively dissimilar forms with qualitatively 

 dissimilar functions remain. 



8. The environment in which plants live operates 

 in different ways, directly as a stimulus or indirectly 

 as a felt necessity and by this means lends to their 

 forms and activities a definite expression of time 

 and place, and thus brings about different adapta- 

 tions. These become permanent through heredity, 

 but are again gradually lost if other adaptations 

 supersede them. 



