88 FIRST GROUP. THALLOPHYTES. 



and are enclosed in an envelope which shows no structure, but is probably formed of 

 swollen hyphae pressed together. Each spore germinates in autumn in the same way 

 as the spores of Entyloma and Tilletia. The sporidia produced from the promycelium 

 conjugate in pairs, and one of the two united sporidia forms a secondary sporidium, 

 which may however be formed directly on a sporidium which has not conjugated. The 

 secondary sporidium puts out a germ-tube, which penetrates into young and sound 

 plants of Trientalis now in their Winter rest. The mycelium formed in the plants 

 spreads during the next year in the new shoots, and developes gonidia on their leaves. 

 While the mycelium produced from the resting-spores thus spreads through the whole 

 plant, that which comes from the gonidia is confined to certain spots on the leaf. Of 

 other forms it remains to mention Thecaphora hyalina. The resting-spores collected 

 into clusters produce a promycelium which is divided by transverse septa. The cells 

 of the promycelium do not however form sporidia (gonidia), as we saw in Ustilago, but 

 develope into filaments, which conjugate in pairs when they meet ; one of the filaments 

 then puts out a new germ-tube. 



3. PHYCOMYCETES '. 



Under this designation De Bary includes the nearly allied groups of the Zygomy- 

 cetes, Peronosporeae, and Saprolegnieae. Their mycelium is copiously branched, and 

 its hyphae are usually without division-walls. The sexual propagation is isogamous in 

 the Zygomycetes, oogamous in the Peronosporeae; the Saprolegnieae have lost the power 

 of conjugation, apogamy having established itself, as will be shown below. Asexual 

 propagation is by non-motile gonidia or by zoospores according to circumstances. 

 The Entomophthoreae are probably allied to the Zygomycetes. 



I. ZYGOMYCETES. The mycelium is a much-branched tube (Fig. 54, Bni), in 

 which transverse septa are formed only when the plant is fully grown and is pre- 

 paring for sexual and asexual propagation. Numerous small nuclei are enclosed in 

 the protoplasm, as is the case with the Siphoneae' 2 . The branches of a mycelium in the 

 Zygomycetes are all the product of a germ-tube from a brood-cell, and can in the 

 course of a few days cover a space of several square centimetres. The Zygomycetes 

 live on organic substances, for example on and inside fruits, on bread and glue, or even 

 on saccharine fluids or dung, from all of which the branches of the mycelium take up 

 their food ; many species grow as parasites on their relatives, withdrawing the contents 

 of their cells by means of organs of suction (haustoria) (Fig. 55, /i). 



Asexual reproduction and multiplication of the mycelia can go on for an unlimited 

 number of generations before favourable conditions occur for the formation of organs 

 of conjugation, that is, for sexual reproduction. The asexually produced brood-cells are 

 formed in two ways. In the Mucorineae thick branches grow from the mycelium and 

 rise erect into the air to a height of some centimetres, and finally swell into a globular 

 shape at their free extremity (Fig. 54, Bg} 3 . N umerous roundish brood-cells are produced 

 from the contents of this globular cell ; they are set free by the bursting of its wall, and 

 germinating at once produce mycelia. In the two other families, the Chaetocladieae 

 and Piptocephalideae, erect gonidiophores branch copiously above and form numerous 

 brood-cells (stilogonidia or gonidia) by abjunction at the ends of their branches, and 

 these produce new mycelia directly as in the Mucorineae. Besides these normal asexual 



1 De Bary, Beitr. z. Morph. u. Phys. d. Pilze, I. (Abh. d. Senckenb. nat. Ges. in Frankfurt a. M. 

 (Syzygites)) ; [see also Vergl. Morph. u. Biol. d. Pilze, Mycetoz. u. Bacter., Leipzig 1884, p. 170, where 

 additional literature is quoted]. Brefeld, Unters. ii. d. Schimmelpilze, Heft II, IV (where other 

 works on the subject are given). [Zopf, Zur Kenntniss d. Phycomyceten, Halle, 1885.] 



2 Schmitz, Ueber d. Zellkerne d. Thallophyten (Abh. d. Niederrh. Ges. 1880). 



3 [Errera, Die grosse Wachsthumsperiode bei den Fruchttragern von Phycomyccs (Bot. Zeil. 

 1884).] 



