THE GYMNOSPERMAE : CYCADALES, ETC. 



773 



integument of which extends in the form of a tube as high as the stamens 

 (Fig. 775). It is usually twisted and expanded at the top into a conspicuous 

 disc, like a stigma. This ovule never matures, and its integumental tube is, 

 moreover, quite different from that of the functional ovules. 



It is not, however, quite functionless, for the nucellus secretes a sugary 

 fluid which exudes on to the " stigma." This is similar to the drop-mechanism 



Abortive ovulf — ^ 







-if. 'M^rMe. 



Fig. 774. — Wehvitschia iniiabilis. Longitudinal section of a male 

 strobilus showing male flowers in the axils of bracts. 



of pollination in the female flower, but in this case it presumably acts simply 

 as an attraction which draws insect visitors to the male flower. 



The stalks of the stamens arise from the edge of a cup-like structure 

 which surrounds the ovule. This may represent a concrescence of their 

 stalks, and it recalls the basal disc of the male sporophylls in Cycadeoidea (see 

 Volume III), and may indeed be a link with that extinct genus. The ring 

 contains six vascular bundles, one going to each stamen. 



The stamens and the " stigma " grow out from between the bracts and 

 protrude from all the ripe flowers of the strobilus simultaneously. 



