s 



GERMINATION OF .-KCIDlo.SPoKEs 



The germ-tube of the secidiospoiv of /'. ('ariri.s can grow bo 

 a Length ten or twenty times greater than the diameter of the 

 spores, and often executes, at Leasl in water, a number ol 

 spiral turns (Fig. 6); it remains nearly of the same diameter 

 t hroughout, or may bear shor( stump} branches here and there. 

 The granular contents of the spore travel along the tube with 

 its growth, remaining always towards the distal end. But 

 unless the germinating spore has fallen upon its proper habitat, 

 the Leaf of a Carex, its attempt at growth comes to an end 

 when its reserve-material is exhausted. 



If, however, the spore has fallen upon a Carex, its germ- 

 tube travels over the surface until it reaches a stoma, through 

 the pore of which it enters the respiratory chamber, forms a 

 swelling just inside as a kind of hold-fast, and then begins to 

 branch and traverse the intercellular spaces, occasionally sending 



an haustorium into the mesophyll-cells 

 (Fig. 7). The cause of its entry is pro- 

 bably the search for water-vapour, since 

 the germ-tube of a Uredine is found 

 (De Bary, 1863; Gibson, 1904) to enter 

 the stomata as freely on another leaf as 

 on one of its proper host-plant, and also 

 to pass through a hole, comparable in 

 size to stomata, in a thin india-rubber 

 membrane which separated it from air 

 saturated with water- vapour (Balls, 1005). 

 But its further growth is influenced by 

 chemotaxis of a more complicated nature : 

 unless the right kind of stimulus is 

 furnished by its host, it cannot form effective haustoria, de- 

 velopment is poor and abnormal, and death soon ensues (Gibson, 

 1904). The resistance of the host to the parasite, shown 

 perhaps by the secretion of destructive enzymes, has also to be 

 considered. Once inside the stomatal chamber, however, the 

 fungus is largely protected from outside influences, such as 

 desiccation : this preservative habit has no doubt contributed 

 much to the wide-spread prevalence of the Uredinales. 



Fig. 7. Haustorium of 

 /'. ( mil- is in cliloro- 

 phvllose cell; m, my- 

 celium ; //, hausto- 

 rium; n, nucleus of 

 cell, x 500. 



