GERMINATION TYPES 211 



the mother cell and after one or more motile stages, become 

 transformed into the assimilatory phase or thallus. In the simplest 

 Phycomycetes this transformation is accomplished by the imbi- 

 bition of water, after which the protoplast increases in volume, 

 although remaining within the stretched parent-cell membrane; 

 more nuclei and more protoplasm are then formed. The spore 

 thus becomes the unicellular, coenocytic, spherical thallus. The 

 transition from germination to subsequent growth is so imper- 

 ceptible that there is little or no evidence of delimitation of the 

 two. Among the higher Phycomycetes, for example, species 

 of Albugo, Phytophthora, Plasmopara, and Sclerospora, the con- 

 tent of the mother cell (sporangium) may break up into intra- 

 sporangial elements (spores), or the sporangium may germinate 

 by the production of a germ tube, depending upon temperature, 

 as one of the controlling factors. 



All spores absorb water and swell as an initial step in germina- 

 tion. In most species a germ tube, the primordium of the myce- 

 lium, is then formed. In some, however, reserve food in the form 

 of droplets of oil can be noted to disappear as the protoplasm 

 moves into the developing germ tube. If the spore contents in 

 their entirety migrate into the hypha, an empty spore cavity 

 devoid of living content is formed. 



In the Erysiphaceae, Peronosporaceae, and Uredinales the germ 

 tube ceases to grow as soon as the reserve food is exhausted un- 

 less a nutritive relationship with an appropriate host plant has 

 been established. If nutrient is available, either from the host 

 tissues or from the culture medium, the germ tube continues to 

 grow, becomes branched, and otherwise assumes the character- 

 istics of the parent thallus. 



The germ tube of the chlamydospores of Ustilaginales and of 

 the teliospores of the Uredinales is, however, a promycelium or 

 basidium. Its growth is determinates The promycelium produces 

 sporidia which may germinate by tube formation. Among the 

 Ustilaginaceae the sporidia may germinate by budding. Among 

 the Tilletiaceae the thread-like elements (so-called sporidia) are 

 regarded by Buller as sterigmata of a specialized type, wmich pro- 

 duce the true sporidia. In species of Taphrina and in Gloeo- 

 sporhtm aridum, Microstroma juglandis, Protocoronospora (Ka- 

 batiella) nigricans , Catenophora pruni, Dematium pallulans, Poly- 



