116 STRUCTURAL BOTANY 



walled cells. It is thinnest (one cell thick) next the 

 partition, and attains its maximum thickness (about 

 five cells) on the side towards the connective (Fig. 40). 

 This layer is of great importance in the dehiscence of 

 the anther. It is owing to the hygroscopic contraction 

 of the fibrous layer, when the ripe anther is getting 

 dry, that the wall is ruptured and dehiscence takes place. 

 If the anther is kept from drying, as sometimes happens 

 in very wet weather, dehiscence may fail to take place. 



d. The Pistil 



The development of the pistil has already been 

 shortly described. The tissue of the carpellary tube 

 is traversed by several vascular bundles, the largest 

 of which are placed opposite the septum. The 

 external epidermis is thickly clothed with hairs of 

 the usual structure ; there are a few stomata. The 

 pistil terminates above in the stigma, the two lobes 

 of which are rough on their inner side, with long 

 papillae, which, as we shall see presently, serve to 

 catch the pollen-grains. 



The ovary contains the ovules, or young seeds (see 

 Figs. 10, 11, pp. 20, 21 ; Fig. 38, G, p. 105). They 

 are numerous, and grow in four rows, two rows to 

 each compartment, on the placentas. 



Each ovule is attached to the placenta by a stalk, 

 the funicle. 



The body of the ovule consists of a central mass of 

 tissue, the nucelliis, 1 continuous with the funicle, and 



1 In the ovule of "Wallflower, when ready for fertilisation, the 

 nucellus is only represented by the emhryo-sac (e] and a small mass 

 of tissue at its base (ri), Fig. 43. 



