THE INITIATION OF STAMINAL ZYGOMORPHY. 697 



right — the flower being viewed from the posterior side — and the stigmatic surface was 

 exposed. In the later stages the condition of the androecium was remarkable. 



A flower with eight fully grown stamens — ^ whose anthers have dehisced — is 

 represented in fig. 11. Of the remaining stamens, one is almost fully elongated, but 

 the other is still very short. The latter is the posterior stamen, the former the 

 extreme left member of the posterior group. The pollen has been almost entirely 

 removed from seven of the dehisced anthers. The stamen whose anther still displays 

 pollen in quantity was the eighth to function, and is the extreme left member of the 

 anterior group. The same flower is represented in outline in fig. 12, and a dotted line 

 has been drawn joining the posterior stamens. Numbers have been placed over the 

 anthers, indicating the order of dehiscence. 



The later conditions of the stamens need not be described in detail. It will suffice 

 to state that, sooner or later, the anthers of the two stamens whose elongation had 

 been delayed most were carried up by filament elongation to the level previously 

 reached by the others, and there dehisced. 



Thus, in the end, the anthers which had stood on one level at a very early stage in 

 the bud were found, when all had dehisced, to be again on one level. 



Morphologically, the staminal zygomorphy had been obliterated. The order of 

 stamen elongation in figs. 1, 6, and 11 is indicated in figs. 21, 22, and 23 respectively, 

 and circles have been placed round the numbers indicating stamens whose anthers had 

 dehisced. 



It was at first expected that an anatomical examination of the anthers of those 

 flowers in which the zygomorphy was pronounced would reveal differences in the 

 condition of the anther-walls, the pollen-grains, or the connectives. No differences 

 were observed in the anthers of expanded flowers, or even in young buds in which the 

 antero-posterior zygomorphy had just been initiated. In all those it was found that the 

 pollen-grains were apparently perfected, and the mechanism of the anther-walls laid 

 down. The main internal details of the anthers had apparently been completed while 

 the androecium was still actinomorphic. The only evident difference in the stamens 

 was in the length of the filaments. 



It should be mentioned at this point that the lateral zygomorphy made its 

 appearance in the later-formed flowers, before the antero-posterior zygomorphy had 

 had an opportunity to become pronounced. In figs. 28 to 33 this point is demonstrated. 

 These diagrammatic figures represent a series of transverse sections through a very 

 young flower-bud. The gynoecium and androecium alone are represented. 



Section I. passes through the lower portions of the united carpals, and the stamen- 

 filaments. Section 11. was taken a little higher in the flower, and the basal portions 

 of two anthers have been traversed. The stamen whose four anther-lobes are 

 represented is the posterior one. In Section IV., taken still higher, six anthers are 

 represented. Five of these belong to the posterior stamen-group. A section inter- 

 mediate in position to Sections II. and IV. is represented in fig. III. Eight anthers 



