300 PROCEEDINGS OF THE ACADEMY OF [1893. 



Now reverting to E. maeulata we find a much greater disparity 

 in the size of the opposite leaves, and necessarily in the size of the 

 strength of the axillary bud. The large leaf, which seems to have 

 no axillary bud has really had one so strong in proportion to the 

 leaf opposite that it has pushed it wholly aside, has succeeded 

 in forming a perfectly straight stem. The straight stem in Euphor- 

 bia maeulata, is really made up, therefore, of an axillary branch 

 which at each node has wholly taken the place of the main axis 

 which has become totally suppressed at each point. 



As, however, the vegetative growth becomes more under the con- 

 trol of the reproductive force, the vigor of the side branches which 

 proceed from the axillary buds along the main stem is checked ; and 

 with this the axial growth develops sufficiently to form a peduncle 

 and flower-head as already noted, and these central axes bearing 

 the flowers get stronger and stronger, just in proportion to the 

 development of reproductive agencies. 



We are taught by these illustrations the great lesson that the 

 power of an axillary bud to draw to itself nutrition at the expense 

 of the main axis and opposite axillary bud is the chief cause of the 

 varying characteristics of the branches. In the same plant it 

 causes a variation from a merely flexuose stem in the lower portion 

 to an almost perfectly forked condition finally — while it equally 

 accounts for a wholly different character of straight main stems in 

 an allied species. 



The exact manner in which an axillary bud can achieve such a 

 power of nutrition as to entirely obliterate and supplant the main 

 axis, and how again that main axis can still again overthrow its 

 lateral competitor and advance sufficiently to become a flower-bear- 

 ing peduncle is yet a grave question which cannot be answered. 

 But a consideration of all the facts brings out the safe conclusion 

 that the achievement of greater power in some buds to advance 

 over others by drawing to themselves nutrition at their expense 

 is a powerful factor in the origin of form. 



As every flower head produces seed, it is safe to assume 

 on my theory that the flowers self-pollinate. An examination 

 shows that this is the case. Long before the involucre unfolds the 

 staminate flowers have scattered their pollen over the pistils of the 

 female flower, thoroughly dusting them. The glands are gener- 

 ously nectariferous, larger and more productive of fluid in E. mae- 

 ulata than in E. hypericifolia. All effort to form a conception of 



