ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 533 



noted differences in their habits of growth. Taking a twig of the last 

 season's growth, in a flowering condition, one or two blossoms might 

 appear alongside of the leaf-bud, in trees of either sex. So far there 

 was no difference. But in the female tree the central or leaf-bud, 

 when it pushed into growth in the spring, made a shoot of several or 

 many inches in length, according to the vigour of the tree or parent 

 branch. In the male tree, on the contrary, the central growth was 

 not more than perhaps a quarter of an inch, forming a mere tuft of 

 leaves on the top of what was a head of male flowers. The immense 

 amount of pollen from the early flowers, forming the great bulk of all 

 the pollen produced by the tree, is scattered before the female flowers 

 open, and is absolutely useless for any purpose of fertilization, or use- 

 less for any purpose of individual benefit to the tree or to the race. 

 These later opening flowers, formed on the wood of last year, are 

 evidently the chief reliance, if not the only reliance, of the female 

 flower for its reproductive energy. 



It may be stated in general terms that a highly vital condition is 

 more closely allied with those attributes which characterize the 

 female sex than with those characteristic of the male, and we may 

 therefore reasonably look for some influence in the female direction on 

 the male flower where these conditions exist. Therefore male flowers 

 on a shoot characterized by a highly vitalized condition, would be 

 likely to resist influences to which they would be otherwise subjected. 

 In short, a male flower on a strong branch ought not to yield as 

 readily to the excitement of heat as one growing on a weak branch. 

 At any rate the fact that the whole of the weak spurs of the maple 

 tree produce nothing but male flowers, and that these male flowers 

 expand at a lower temperature than the females do, is conclusive as to 

 the law, whatever answer the objection may receive. This law, thus 

 demonstrated, will be of great practical value to culturists. 



As regards the influence which these facts must have on questions 

 of dichogamy, there need not necessarily be any constant rule in 

 the production of proterandrous or proterogynous flowers. We might 

 expect to find proterandry prevailing to a greater extent in plants 

 growing where there was a more constant succession of warm and cool 

 days, than in the same species growing where the climate is not what 

 is called changeable, that is to say, where the temperature is regularly 

 low until the regular spring season has arrived, in which there would 

 not be much difference in time between the advance of stamens or 

 pistils. 



In conclusion, the author considers that if he may be allowed to 

 generalize from this experience with the maple tree, the following 

 principles are proved : — 



Male flowers do not appear on female maple trees till some of its 

 vital power has become exhausted. 



Branch-buds bearing female flowers have vital power sufficient to 

 develope into branches. 



Branch-buds bearing male flowers have not vital power enough 

 to develope into branches, but remain as spurs, which ever after produce 

 male flowers only. 



