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 



a 



FIG. 381. 



Two Teleutfl-spores of Puccinia 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) . Very 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 ; 



