3 6 4 



DIVISION III. MODE OF LIFE OF THE FUNGI. 



perforation of the wall every trace of the proceeding has disappeared with the exception 

 of a small projection which attaches the tube within the cell to the place of entrance. 

 The tube now grows and ramifies inside the epidermal cell, and ultimately pierces 

 through the inner wall of the cell and developes a mycelium in the tissue beneath it 

 (Fig. 164). 



The majority of the intracellular Chytridieae, especially the Synchytrieae, show 

 the same extremely slender perforating process, the same transference of the protoplasm 

 of the spore, and the same ultimate disappearance of the wall of the empty spore and 

 the perforating process. 



In some species the penetration begins with an indentation in the membrane, 

 which must be accompanied with a corresponding local extension of the surface ; the 



indentation forms a sheath of 

 a certain depth round the 

 tube, and is subsequently 

 pierced at the apex, showing 

 sometimes characteristic struc- 

 tural peculiarities. This is the 

 process in the case of Leitgeb's 

 Completoria (see page 160), 

 Peronospora Radii and some 

 other species. 



The above phenomena of 

 penetration on the part of 

 germ-tubes and haustoria take 

 place only in the membranes 

 of the host which happen to 

 be suitable to the parasite. 

 The germ-tubes when placed 

 on other species usually perish 



tans ; zoospore germinating and germ-tube penetrating into an epidermal cell (cut without penetrating intO the 



cells. I have only once ob- 

 served an exception to this 



rule ; in this case the germ-tubes of Peronospora pygmaea, Ung. which lives on 

 species of Anemone penetrated into the epidermal cells of Ficaria ranunculoides, 

 but died away there at once. The thickness or other structural characters of the 

 membranes of the host, which vary at different ages and in different individuals, 

 are in most cases of little moment, though young and delicate membranes are more 

 easily and more rapidly pierced than those which are strongly thickened. In certain 

 cases, however, perforation is possible only in certain states of development of 

 the membranes of the host, and these states have some relation to the age. The 

 Synchytrieae for example only penetrate into the epidermal cells of young leaves of 

 their host which are not fully unfolded ; the sporidial germ-tubes of Endophyllum 

 Euphorbiae only into the epidermal cells of the young foliage of Euphorbia amyg- 

 daloides which are formed in the same summer with themselves, not into the leaves 

 of the previous year which have gone through the winter ; and many Ustilagineae 

 only into parts of young germinating host -plants. 



FIG. 164. a Uromyca appendiculatus. Sporidia germinating on the epidermis 

 . of the stem of Faba Tiulgaris, Mch. ; the germ-tube of one sporidium x has pene- 

 trated into a cell of the epidermis and grown considerably. * Phytofhthora infcs- 



ting and germ-tube penetrating into an epidermal 



through transversely) of the stem of a potato. The preparation made seventeen 

 hours after the dissemination of the spores. Magn. 390 times. 



