240 



BOTANY OF THE LIVING PLANT 



to contain Jour loculi, or pollen-sacs, two being placed on eitlier side 

 of a central connective, which is simply a continuation upwards of 

 the filament. A single vascular strand which traverses the filament 

 IS continued upwards into the anther, where it fades out usually 

 without any branching (Fig. 192, A). However unlike a foliage leaf 

 the stamen so constructed may appear to be, there is no reasonable 

 doubt of its foliar nature. It arises from the axis like a leaf, and in 

 acropetal succession, while in " doubled " flowers it may not un- 

 frequently be seen to be transformed into a petal, or even into a green 



Fig. 193. 

 Lobe of anther ol Ca/i/ia cut transversely, showinj,^ two pollen-sai?s at maturity, 

 wittt the fibrous layer immediately below the epidermis. For details see text. 

 ( .'. 100.) F. O. B. 



leaf of the foliage type. But better evidence is obtained by comparison 

 of earlier fossil Seed-Plants, in which the organs bearing pollen-sacs 

 are actually leaf-like. 



It may then be accepted that the stamens are leaves, specialised for 

 bearing pollen-sacs or micro-sporangia. Each pollen-sac is enclosed 

 til! it is ripe by a wall consisting of several layers of cells. In most 

 stamens the slit of dehiscence runs longitudinally, following the line 

 where the walls of the two sacs of one anther-lobe join with the 

 septum that separates them (Fig. 193). There the cell-walls arc thin, 

 and the cells themselves arc rounded off by intercellular spaces, so 

 that they easily come apart. The slit thus formed gapes widely, owing 

 to the action of the walls of the pollen-SLics. Below their superficial 

 epidermis lies a layer of fibrous cells, the inner cell-walls of wliich are 

 thicker than the outer, while fibrous bars running outwards along 

 their lateral walls prevent radial collapse. The eft'cct on these cells of 



