204 PROCEEDINGS OF THE 



will be hardly any traces of alcohol in the liquid. On the other 

 hand, if there is sufficient nitrogenous matter, the fermentation goes 

 on, accompanied by the production of a more highly-developed form 

 of the mycelium, consisting of elongated filaments known as the 

 "Vinegar Plant." This organism, and of course the "Yeast 

 Plant" as well, seem to be but imperfectly developed forms of 

 several fungi which are usually regarded as specifically distinct. 



This affords one of the few instances in which the lower fungi 

 prove of any economic importance; but it is not difficult to find 

 many of these plants that cause much mischief and devastation. 

 One of them (Peronospora infestans) occasions the potato blight, 

 and as illustrative of parasitic action in general, it is worthy of 

 consideration, especially as so much is now known of its modes of 

 reproduction. Its mycelium possesses the power of destroying the 

 starch and other substances in the tissue of the potato, and of 

 absorbing part of the products; but its adaptations for reproduction 

 are especially noteworthy. Branches of the mycelium break from 

 the interior of the leaf into the air usually through the stomata. 

 These threads ramify, and at the tips of the branches bear two 

 kinds of fruit — 1st, simple spores or conidia; and 2nd, vesicles 

 containing zoospores. A simple spore falling on a suitable nidus 

 sends mycelial filaments through the stomata into the interior of 

 the plant, and thus germinates. The vesicle, on the other hand, 

 on the application of moisture, sets free a swarm of zoospores, 

 varying in number from half-a-dozen to upwards of a dozen, each of 

 which is furnished with two lash-like tails. These zoospores move 

 rapidly about like animalcules for about half-an-hour after emerging 

 from the vesicle, when they enter the stomata of the potato leaf 

 (on which it is assumed that they are moving about), and there 

 germinate. One square line of the surface of such a leaf is 

 calculated to be capable of producing 3,270 acrospores, each 

 yielding at least 6 zoospores, so that we have thus 19,620 repro- 

 ductive bodies from that small space. When they cease to move, 

 their lash-like tails disappear, and the mycelium proceeding from 

 them commonly penetrates the cellular tissue in twelve hours at 

 farthest. The fruit-bearing thread bursts out, usually through the 

 stomata, and perfects its fruit in from fifteen to eighteen hours. 

 Hence it is clear that countless myriads may be produced in a few 

 days from a single germ. Dr. de Bary traced the development of 

 the zoospores from the earliest stages, and found that the brown 



