112 



THE WHEAT PLANT 



They usually measure 3 to 4 mm. long and -5 to i mm. across, and are 

 green when young, becoming yellow or pink when ripe. Each lobe 

 contains two loculi, the tissue between which breaks down at the time 

 of dehiscence. 



The filament of the stamen before anthesis is cylindrical, of uniform 

 thickness, and from 100 to 120 /x in diameter. It consists of long paren- 

 chymatous cells -5- -8 mm. long and 9-12 p in diameter. In the centre 

 is a small vascular strand possessing one or two annular tracheae 8-9 fj, in 

 diameter, with closely arranged rings or an occasional spiral thickening. 

 When flowering occurs the filament grows rapidly, becoming very irregular 

 in thickness, and the rings in its vessels greatly separated from each other. 

 The tissue of the connective is parenchymatous, with a slender vascular 

 bundle resembling that of the filament running through it ; in the 



epidermis investing it on the 

 dorsal side are two rows of 

 simple stomata. 



The epidermis of the anther 

 lobes is composed of narrow 

 cells with their long axis par- 

 allel to the long axis of the 

 anther. Each cell is from 50 

 to 80 n long and 10 to 15 /j, in 

 diameter, its outer wall having 

 a cuticle which is covered with 

 fine wavy longitudinal lines 

 (c, Fig. 86). 



Immediately within is the 

 endothecium (b, Figs. 85, 86, 

 87), consisting of narrow cells about 60 ^ long and 10-12 ^ broad with 

 their long axes arranged across the cells of the epidermis : a short time 

 before dehiscence of the anther the walls of these cells develop character- 

 istic short pyriform thickenings, which project at right angles from the 

 wall into the cell lumen (b, Fig. 86). 



The pollen-grains are smooth and spherical, or slightly oval, somewhat 

 irregular in size and form : their diameters measured in a dry state as shed 

 from the anther are 



T. aegilopoides . 37-45 \ T. dicoccum . 48-52 T. compactum . 52-61 

 T. monococcum . 37-45 T. durum . . 48 T. vulgare . . 61-65 

 T. dicoccoides . 44-64 T. turgidum . 57-65 j T. Spelta . . 65 



In the exine is a circular or oval pore closed by a minute lid 4-5 JJL in 

 diameter (Fig. 88), which is pushed off when the pollen tube develops. 



Within the pollen-grain are large numbers of minute oval starch- 

 grains from i to 4 /z long ; these are more abundant in the half of the grain 



FIG. 88. Pollen-grains showing pore in the exine. 



