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A TEXTBOOK OF THEORETICAL BOTANY 



occur, especially during the ripening of heavy fruits such as those of 

 Cucurbit a. 



If the structure of the pedicel is relatively simple, it is quite otherwise 

 with the floral receptacle itself. Here we have to deal with a highly con- 

 densed structure upon which are crowded together a large number of varied 

 appendages, each with a distinctive vascular structure. Moreover, the axis 

 has only limited or determinate growth, that is to say it is without any 

 permanent meristematic apex to which the development of structures can 

 be related, as in a vegetative axis. The abrupt ending of the floral axis at 

 the uppermost carpel is apparently due to inhibition from within, not to 

 starvation. It has two elements of great value from the evolutionary stand- 

 point; in the first place, the retention of the reproductive appendages within 

 the protective limits of the calyx, and secondly the freedom of the ovules 

 from the metabolic competition of any superior organs. The cessation of 

 growth is not inevitable, as may be seen from the anomalous development 

 known as proliferation, found for example occasionally in Rosa, in which 

 the floral axis continues to grow, reverting to the vegetative condition and 

 forming a leafy shoot which may eventually produce a second or even a 

 third flower. 



The vascular anatomy of the axis in the hypogynous flower is simpler 

 than that in the epigynous flower, which we will consider later. Even in the 

 simpler case however the variation is so great that the structure can only 

 be described in the most general terms. As the slender pedicel enlarges 

 into the bulbous or conical receptacle, the ring of vascular elements also 

 enlarges proportionally and the individual bundles usually broaden tangen- 

 tiallv so that there is an almost continuous or sometimes a wholly continuous 



Fig. 109 1. — A series of sections, of which A is the|lo\vest, showing vascular changes from the 

 pedicel to the receptacle. C shows a compound, fused bundle. At D, this has split to 

 give off the median trace of a sepal. E, The lateral bundles have also split and given off 

 the two sepal laterals, leaving three gaps. F, The lateral gaps have closed and the three 

 sepal traces are moving outwards. Caltha pahistris, somewhat diagrammatic. {After 

 Smith.) 



