92 FIRST GROUP.— THALLOPHYTES. 



insect is different. The germ-tube does not swell, as in Empusa, into a globular cell 

 which afterwards sprouts like the cells of the yeast-plant, but developes into a much- 

 branched mycelium divided by transverse septa, which in the space of five days 

 usually spreads entirely through the fatty substance of the caterpillar and so wastes it, 

 that the lightly-stretched skin of the insect ultimately contains nothing but a dense 

 hyphal tissue with the tracheae and intestines. The fungus-mummy is then secured to 

 the substance on which it lies by tufts of hyphae which break through on the under 

 side, while a number of branches of the mycelium come out through the upper surface, 

 ramify and give rise at the extremity of every branch to a gonidium which is abjected 

 and can infect a healthy insect in the same way as in Empusa. After a series of 

 asexual generations resting spores make their appearance ; their presence in the dead 

 caterpillar is shown by its not stiffening in death, but continuing flaccid. According to 

 Nowakowski these spores are formed by conjugation ; two cells put out processes 

 towards one another, as we see in the Conjugatae, and these processes unite. On one 

 of them, or on some portion of the conjugating cells, a protuberance is formed into 

 which the protoplasm moves ; the protuberance becomes globular in form (zygospore) ', 

 and being cut off by a transverse septum becomes the resting spore, the germination of 

 which has not yet been observed ; it has a very thick cell-wall which is differentiated 

 into an exosporium and an endosporium. 



2. The PERONOSPOREAE ^ according to De Bary's latest researches, include the 

 genera Pythiiini., P/ijtophf/iora, Pt'?-otiospora, Sclerospora and Cystopiis ; they are for 

 the most part parasites living in the interior of living plants, though the genus Pythium 

 contains species which can live as saprophytes as well as parasites ; P. De Baryantim, 

 for instance, often attacks and kills the seedlings of Dicotyledons, but can vegetate 

 equally well in dead plants and animals ; P. vexans, on the other hand, lives as a 

 saprophyte in potato-tubers, but cannot penetrate into the tissue of the living plant. 

 Peronospora and Cystopus inhabit the juicy parenchyma of living Dicotyledons ; the 

 much and irregularly branched mycelium spreads widely in their intercellular spaces, 

 thrusts a number of suckers {haustoria) into the parenchymatous cells of the host, and 

 takes their contents for its own support. The vegetative body, the mycelium, is at first 

 a single tube which is not divided by transverse walls, and numerous nuclei may be seen 

 in its protoplasm. At a later period, when the organs of propagation are being formed, 

 transverse walls are found in it at irregular intervals. At the beginning of the period of 

 vegetation propagation is effected almost exclusively in the asexual way by the formation 

 of non-motile gonidia or of swarm-spores, in Pythium of swarm-spores. Ultimately, 

 under suitable conditions of nutrition, oospores are formed sexually ; in many species 

 of Pythiutn indeed they may make their appearance quite at the commencement of the 

 vegetative period. When swarm-spores are formed in Pythiinn the whole of the pro- 

 toplasm of the usually spherical sporangium issues forth and then divides into a number 

 of swarm-spores. Pythium De Baryanum has not only these zoosporangia but also 

 resting gonidia, which are of exactly the same appearance as the zoosporangia but do 

 not produce swarm-spores ; they persist after the vegetative portion of the Fungus has 

 died away, and develope germ-tubes in germination ; in this case then zoosporangia 



' Brefeld (Schimmelpilze, Heft IV.) does not consider the process in the formation of the resting 

 spores to be the same as that in the formation of zygospores in the Mucorineae, &c., but to be an asexual 

 one, because the resting spores are formed also on filaments which have not conjugated with others, 

 and coalescence occurs on purely vegetative branches of the mycelium of many Fungi. 



^ De Bary in Ann. d. sc. nat. 4® serie, T. XX ; Id., Untersiich. uber die Peronosporeen u. 

 Saprolognieen u. die Grundlagen eines natiirlichen Systems der Pilze, in De Bary u. Woronin, Beitr. 

 z. Morph. u. Phys. d. Pilze IV. Reihe (Abdr. a. d. Abh. d. Senckenberg. nat. Ges. Bd. II. Frankfurt 

 1881) ; Id. Zur Kennln. der Peronosporeen (Bot. Zeit. 1881) ; [also Vergl. Morph. u. Biol. d. Pilze 

 Mycet. u. Bacterien, Leipzig 1884. — Marshall Ward, Observations on the genus Pythium (Q. J. M. S. 

 Oct. 1883).] 



