232 THE STRUCTURE OF FLOWERS. 



SO that normally hermaphrodite flowers may become uni- 

 sexual, and every possible degree between these two extreme 

 cases can be met with in nature and cultivation. The 

 problem, thei'efore, is to discover what the immediate causes 

 may be in each case which stimulate or suppress the energy 

 required for the proper development of the stamens and 

 pistil respectively. 



There appears to be a closer bond between the stamens 

 and corolla than between the two kinds of essential organs 

 themselves ; * thus, if the corolla degenerate, the antipetalous 

 stamens at least tend to follow suit, as in the Alsivece. On the 

 other hand, the fii'st tendency towards " doubling " appears 

 in a more or less pronounced petalody of the androecium. 



As petals are a nearer approximation to foliar organs, 

 the above means that vegetative energy is more prone to 

 affect the stamens, when from some cause they have first 

 begun to lose their proper function, than the pistil. 



The pistil may fail in its development from two classes 

 of causes : either from an undue display of the vegetative 

 vigour, as in completely double flowers — though it may be 

 unaffected in a partially double one ; or else from excessive 

 feebleness, under which a flower may succeed in making the 

 androecium, but has not sufficient energy to develop the 

 gynoecium ; as, e.g., often takes place in the flowers of the 

 Umbelliferce at the close of the season. 



There is no absolute rule in these matters, and differences 

 result from various degrees of energy at the disposal of the 



* A study of the vascular system of flowers and their axes bears this 

 out, as the provision made for the stamens usually arises from the 

 perianthial cords, while that for the pistil is mostly isolated off in rather 

 a more marked and independent manner. Exceptions occur, as in 

 Ballofa nigra, in which the four stamens originate from the same cords 

 as those of the placentas. 



