3 66 



GENERAL BIOLOGY 



year are past, the bone beneath the burr begins to be eaten 

 away and absorbed, through the activity of certain large 

 bone-eating cells, and, the base of attachment being thus 

 weakened, the beautiful antlers are shed; the scarred sur- 

 face skins over and heals, and only the hair-covered pedicel 

 of the antlers is left." 



Antler development on the part of the male is no less 



remarkable, al- 

 though far less im- 

 portant, than the 

 organic response 

 on the part of the 

 female that follows 

 upon fertilization 

 of the egg and re- 

 sults in the produc- 

 tion and nurture of 

 the young. Figure 

 213 is intended to 

 show how quick is 

 this response to 

 fertilization in the 

 common spreading 

 dogbane. If a 



flower fail of fertil- 



ization it dies, but 

 if fertilized, the fruit which then develops from it may 

 reach full size before the last of the flowers on the same 

 peduncle have faded. 



These examples of organic activity, suddenly and inter- 

 mittently recurring, are the results of internal (perhaps 

 orthogenetic) tendencies. But the reserves of develop- 

 mental power which organisms possess may be tapped by 

 outside agencies as well. Gall insects for example, have 



FIG. 213 New seed pods of the spreading dog- 

 bane (Apocynum), showing quick response to 



fertilization. 



