FUNGI. 245 



at once forming a filament in germination. The zoospores of Peronospora infestans are 

 firmly attached, after swarming, to the cuticle of its host, surround themselves with a 

 thin membrane, and penetrate by a small hole the outer wall of the epidermis (Fig. 

 168, i/, j/>), through which the germinating filament penetrates into the epidermis-cell 

 with the whole of the protoplasm of the zoospore, and then, again piercing through the 

 wall of the epidermis-cell, reaches the intercellular space. The zoospores of Cystopiis 

 candidus are firmly attached near the stomata and push their germinating filaments into 

 its orifice, and thus find their way at once into the intercellular space ; but unless the 

 spores have been sown upon the (green) cotyledons of the host {Lepidium sati'vum^ Cap- 

 sella) they do not develope a mycelium. When the mycelium has once been formed in the 

 parenchyma of the host, it continues to grow in it, and finally often spreads through the 

 whole plant, putting out its conidia-bearing branches at various places in the stem, leaves, 

 or inflorescence. In this manner the (unicellular) mycelium of P. infestans, for instance, 

 can even hibernate inside the tubers of the potato, to undergo further development into 

 germinating filaments in the following spring. The sexual organs of the Peronosporeae 

 are developed in the interior of the tissue of their host. Spherically dilated ends of 

 branches of the mycelium shape themselves into oogonia (Fig. 169, A, og\ in each of 

 which an oosphere is formed out of a definite portion of the protoplasm {B, os). From 

 another branch of the mycelium a branchlet grows towards the oogonium, swells, and 

 becomes closely attached to it ; and the thicker part becoming separated by a septum 

 (just as takes place with the oogonium itself), developes into an Antheridium. As 

 soon as the oosphere is formed, a fine branch of the antheridium (5, ««) reaches it 

 by penetrating the membrane of the oogonium. After fertilisation the oosphere be- 

 comes surrounded by a coat which thickens and forms an external rough dark-brown 

 layer (the Exospore) and an inner one (the Endospore). These oospores remain dor- 

 mant through the winter and then germinate ; in the case of Peronospora Falerianella, 

 they form a mycelium directly on moist ground ; those of Gystopus, however, produce 

 zoospores, the endospore (/) forces itself like a bladder out of the ruptured exospore 

 (Fig. 169, F), and then bursting, the zoospores (G) are set free, which behave in exactly 

 the same manner as those produced from conidia. 



(3) Among Mucorini\ Rhizopus nigricatis {Mucor stolonifer') may be specially men- 

 tioned. It infests dead or dying parts of plants, especially fleshy fruits, which quickly 

 decay in consequence of its attacks. The mycelium is from i to 3 cm. long, and forms 

 stolon-like filaments, which are closely attached to the substratum by root-like branches 

 that afterw^ards become septate, while each of the ascending branches 2 to 3 mm. in 

 height bears a sporangium. The ends of these branches swell up into a sphere and 

 become filled with protoplasm ; the septum which separates this swelling from the 

 branch becomes arched convexly into the cavity of the sporangium, in which numerous 

 small spores now arise. These are set free by the giving way of the wall, and ger- 

 minate only upon a substratum capable of nourishing them (not in pure water) ; putting 

 out at once a germinating filament. They can, however, preserve their germinating 

 power for months, if kept dry. When the mycelium has produced a number of spo- 

 rangium-bearing filaments, the fomiation of the Zygospores begins beneath the white felt- 

 like texture formed by it ; where two of the firm mycelium-filaments touch, each puts 

 out a swelling which is in close contact with that of the other. Both grow in this manner 

 to a considerable size, and assume the form of a club ; a septum then forms in each, by 

 which the thick end is cut off as a conjugating cell. One of the two conjugating cells, 

 which are in contact for some distance, is smaller than the other ; the wall which 

 separates them is then absorbed ; and the two cells coalesce into a single cell (the 



^ De Bary und Woronin, Beitrage zur Morph. u. Phys. der Pilze, p. 25. Frankfort 1866.— On 

 Pilobolus crystalli?ms, cf. Cohn, Nova Acta Acad. Nat. Curios, vol. XV, pt. i. p. 510. [Klein in 

 Pringsheim's Jahrb. vol. VIII. — Van Tieghem and Le Monnier, Ann. des Sci. Nat. 1873, vol.XVlL] 



