. The British rust fungi (Uredinales), their biology and classification. Uredineae. 8 GERMINATION OF ^CIDIOSPORES The germ-tube of the secidiospore 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 habita
. The British rust fungi (Uredinales), their biology and classification. Uredineae. 8 GERMINATION OF ^CIDIOSPORES The germ-tube of the secidiospore 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 Garex, its attempt at growth comes to an end when its reserve-material is exhausted. If, however, the sjDore 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 Avhich separated it from air saturated with water-vapour (Balls, 1905). 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 contribute
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