364 DIVISION III.—-MODE OF LIFE OF THE FUNGI. 
perforation of the-wallevery trace ofthe 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 Dean 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 166), 
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 








FIG. 164. a Uromyces appendicul Sporidia inating on the epid x é 
of the stem of Fava vu/garis, Mch.; the germ- ‚tube of one sporidium x has pene- on other species usually perish 
trated into a cell of the epidermi and grown 5b Ph. hth infes- 


tans; zoospore germinating and germ-tube penetrating into an epidermal cell (ut without penetrating into the 
through transversely) of the stem of a potato. The preparation made seventeen 
- hours after the dissemination of the spores. Magn. 390 times. 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. 
