8 GERMINATION OF ACIDIOSPORES 
The germ-tube of the ecidiospore of P. Caricis can grow to 
a length ten or twenty times greater than the diameter of the 
spores, and often executes, at least in water, a number of 
spiral turns (Fig. 6); it remains nearly of the same diameter 
throughout, or may bear short stumpy 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 Carew, 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 
Fig. 7. Haustorium of Membrane which separated it from air 
P. Caricis in chloro- saturated with water-vapour (Balls, 1905). 
Lis anes But its further growth is influenced by 
rium; m, nucleus of chemotaxis of a more complicated nature: 
cell, x 500. : . : E 
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 ipside 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. 
