110 NOMAD FUNGI. 



conceive a doubt about the truth of the tlieory in the other or autcecionn 

 species, where the various forms appear on the same plant. 



This Puccinia (viz.. fimmiiiis), then, begins its Hfe in sprin.ij as an 

 CEcidium, or cluster-cup, on the leaves of Berberis, usually ujion 

 BerherU rulfiaris, the common wild barberry, but also upon most of 

 the cultivated forms. If the spores of this, when ripe, be taken and 

 sown upon the leaves of a young wheat plant, which has never been 

 exposed to the risk of any accidental infection by other spores, it 

 germinates, throwing out a germ-tube. This germ-tube travels over 

 the leaf, searching for a stomate into which it may enter. As it 

 elongates it assumes a spiral form. Sometimes after making four or 

 five turns from left to right, it will reverse its motion, and make the 

 succeeding turns from right to left. It is obvious that by these means 

 it adds greatly to its chance of finding and entering a stomate ; in fact, 

 this motion, and the object of it, are very similar to that which Dr. 

 Darwin has so recently made known with reference to the growing 

 radicle of flowering plants. Mr. C. B. Plowright, to whose experiments 

 I am now referring, says that all the trouble he took in conducting his 

 experiments was fully repaid by the intense pleasure of watching this 

 germ-tube feeling its way over the epidermis of the wheat-leaf in 

 search of the opening by which alone it could enter in. Having 

 obtained an entrance, the tube, by repeated branching, forms a myce- 

 lium, which increases within the plant tissues, and at last the ends of 

 the hyphsB turn upwards towards ths surface, forming an hyraenmm 

 or layer of basidia. Each basidium, by constriction from its extremity, 

 forms a uredo-spore, which assumes a deep yellow or orange colour. 

 As the mycelium continues branching, and each branch produces a 

 spore, the increasing mass at last ruptures the epidermis, and the 

 spores escape. Now these spores, like those of the CEcidium, have 

 only a thin cellulose coat ; they are evidently adapted for germinating 

 immediately. This is in fact what they do ; each uredo-spore, if it 

 falls upon a leaf of the wheat-ialant, germinates at once, throws out a 

 germ-tube, which searches as before for a stomate by which it enters, 

 and forms a new inycelium. which produces again uredo-spores. By 

 repetition of this process, the fungus spreads itself fi-om plant to plant 

 over a large area. The spores are easily dispersed by wind and rain. 



But these spores, though evidently adapted by their vast numbers, 

 their ready dispersion, and the ease with which they germinate, for 

 effecting their object, namely — the rapid diffusion of the fungus, 

 evidently do not furnish the best conditions for prolonging its life 

 through the trials of winter, and preserving it to afilict the agricul- 

 turist in another year. These thin-coated spores lose their power of 

 germination in a few weeks. Now see what the fungus does. Know- 

 ing what is coming, it takes the best means of ensuring its safety by 

 producing spores calculated to resist the adverse influences of winter 

 weather. Like a wise mother, it clothes its offspring in a warm great- 

 coat. In fact, it produces resting-spores, as do so many other organ- 

 isms well known to the microscopists in this room. The same 



