THE ANGIOSPERMAE 1167 



shown in some species of Ranunculus, where an increase or decrease in the 

 number of stamens is associated with a reverse change in the number of 

 petals. 



Ahhough the two-fold, convergent origin of the two components of the 

 perianth is supported by many observations in flowers of various families, 

 it would be a mistake to regard it as a universal rule. Some of the spiral 

 flowers of the Ranunculaceae suggest, by the absence of a clear demarcation 

 between sepaloid and petaloid perianth members, a common origin in such 

 cases from the androecium. In some of the small flowers of Eagales, on 

 the other hand, it is difiicult to distinguish between perianth segments and 

 bracts, both appearing to have a common foliar nature. The same is true of 

 some spiral flowers also, e.g., Calycanthus. As the biological functions of 

 the perianth are so variable in different families, it should not be surprising 

 that its morphological nature may also be variable. 



i 



THE ANDROECIUM AND THE STAMENS 



The position of the androecium, by which name we signify collectively 

 the stamens, or the " male attire " of the flower, as some early authors 

 called it, is typically between the innermost petals and the outermost 

 carpels. It forms thertfcre the lower zone of that pyramid of reproductive 

 organs which constitutes the second of the two main regions in the flower. 

 Together with the gynoecium it makes up what are often called the " sexual " 

 or " essential " organs. 



We must emphasize here that to call either a stamen or a carpel a sexual 

 organ is a misnomer. Both are sporophytic structures, bearing sporangia 

 and producing spores. The confusion was natural enough in earlier days, 

 because the extremely reduced gametophytes remain enclosed within the 

 spores, and the existence of an alternation of generations was unsuspected. 

 There is no excuse for such an error at the present day. 



The stamens bear -microsporangia and by common consent they are 

 usually equated to the microsporophylls of the Pteridophyta and Gymno- 

 spermae, though we shall have to consider later whether they are in fact 

 descended from single leaf structures or from a branch system. 



The stamens of some of the least specialized flowers are arranged 

 spirally, following the same genetic spiral as the perianth on one side and the 

 carpels on the other. No question of the alternation of parts therefore 

 arises. A comparatively small shift in the divergences or intervals between 

 the rudiments of the lowermost stamens would disjoin the continuous 

 spiral into a series of separate parastichies (see p. iioi), each pursuing a 

 spirally curved path around the floral receptacle, thus creating a hemicyclic 

 flower, such as that of Nigella. The commonest numbers of these para- 

 stichies are 8 and 13. When the higher number is present, especially if the 

 stamens are very numerous, as in Aquilegia and in some species of Helle- 

 borus and Anemone, the vertically superposed stamens form close vertical 

 rows, or orthostichies, which are more conspicuous than the oblique 

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