700 MR JOHN MCLEAN THOMPSON ON 



of time, the development which has just been outlined is believed by the writer to be 

 normal for the species. 



The sizes of the filament-cells were carefully measured at all the stages figured, and 

 an examination of those stages showed that the great increase in stamen-length after 

 the completion of the anther-wall was not due to any appreciable increase in the 

 number of cells in the filament rows, but primarily to the elongation of those cells 

 which were already present. 



Cell -division was, of course, necessary for the production of the large number of cells 

 present in the filaments of full-grown stamens, and it will be understood that the 

 compacting of cells at the top of the filament, mentioned in the description of fig. 27, 

 and further pointed out in fig. 34, was due to a localisation of this merismatic activity. 



The examination of the stamens of Staphylea jnnnata was rendered easy by the fact 

 that the androecium consists of only five stamens forming a single cycle. 



The marked increase in length of stamen-filament in flowers with large stamen 

 numbers may be illustrated by a brief examination of flowers of Aquilegia vulgaris L. 

 In the wild flowers of this species which were examined, and from which the 

 accompanying photographs were taken, the stamens numbered about seventy, forming 

 about seven approximate cycles. The order of stamen-elongation and anther-dehiscence 

 was basipetal. 



In fig. 18 the first group of stamens will be seen to have elongated, and their 

 anthers to have dehisced. The anthers of the remaining stamens are undehisced, and 

 the very evident space which separates them from their dehisced neighbours is mainly 

 due to the filament-elongation already mentioned. 



In fig. 17 it will be seen that the second group of stamens are elongating, and that 

 dehiscence is progressing in their anthers. 



A more advanced stage is represented in fig. 19, in which it will be seen that, 

 although various degrees of filament- elongation have been attained, anther-dehiscence 

 has taken place only in those stamens whose filaments have reached their maximum 

 length. 



In the case of those flowers it was also found that filament-elongation, prior to 

 anther-dehiscence, was primarily due to the elongation of the cells already present in 

 the filaments. 



Returning now to the androecium of Greijia Sutherlandii, it should be at once 

 stated that, while the initial staminal actinomorphy persisted, the cell-rows which 

 composed the filaments consisted of fewer cells than were found in the filaments at 

 a later stage. Definite numbers are not quoted, because, as has been already stated, 

 the rate of the progression of zygomorphy in no single flower examined could be said 

 to be typical for the flowers as a whole, and further because, although an external 

 examination failed to reveal diff"erences in the conditions of stamens in flowers which 

 appeared actinomorphic in their androecium, the anatomical examination showed 

 diff"erences in the merismatic condition in the filaments. A merismatic zone, however, 



