446 



BOTANY OF THE LIVING PLANT 



that the germ-tubes emerge when grown in water (Fig. 378). If this 

 germination takes place on a wet leaf of wheat, the tube growing over 

 the surface finds entry by a stoma (Fig. 379), and at once gains access 

 to the nutritive cells. In about a fortnight the infected spot will be 

 producing fresh uredo-spores. 



The Teleuto-spores arise from the same spore-bed later in the 

 season. They differ in being closely packed and firmly attached, as 

 well as in structure. Each spore is spindle-shaped, and is partitioned 



Fig. 381. 

 Two Teleuto-spores of Piiccinia germinating. In the one to the left each cell has 

 given off a promycelium [a, a) ; to the right only the lower cell has done so, and the 

 promycelium has given rise to four sterigmata, bearing sporidia (s, s). \''ery highly 

 magnified. (After Marshall Ward.) 



into two cells, each with a dark brown coat (Fig. 380). Like other cells 

 of the mycelium and the uredo-spores themselves, each cell contains 

 two nuclei. They do not germinate till the following spring. In 

 March or April, after a few hours in water, each cell puts out a delicate 

 tube (Fig. 381). This, after segmenting to form four distal cells, 

 constitutes what has been called tHe promycelium, which is a septate 

 basidium. The first step is the fusion of the two nuclei : then follows 

 a division into two and into four — in fact a tetrad-division, followed 

 by partitioning of the four cells. Each cell then forms a process, or 

 sterigma, on the end of which a swelling appears, and into it the 

 protoplasm and nucleus pass. These are sometimes called sporidia; 



