CHAPTER VII.—PHENOMENA OF VEGETATION.—PARASITES. 393 
fenced off from the parasite by a pellicle which forms a close sheath round the intruder. 
Assimilation, metabolism, and even growth of the cell continue often for weeks and 
months, the latter in some cases longer even than when there is no parasite present. The 
cell succumbs comparatively slowly to the influence of the parasite. This pheno- 
menon, which again shows many shades of difference in different cases, is everywhere 
common, as in the Peronosporeae and Uredineae, in the haustoria of the Erysipheae, 
in epidermal cells attacked by Synchytrium, in the Saprolegnieae when attacked by 
Olpidiopsis (see on page 166), and some others. Leitgeb in his work on Comple- 
toria ! calls attention to this subject, which has often been observed and mentioned. 
He finds also in the continued activity of the protoplasmic body when thus attacked 
the explanation of the fact, which has likewise been often described, that mycelial 
hyphae, which grow transversely through a cell, are enclosed in a sheath of cellulose 
which is continued without interruption into the membrane of the cell attached, or 
springs from it. This sheath is often developed in a remarkable manner on the 
endophytic mycelia of the Ustilagineae ?. 
The piercing of the membrane after the Fungus has made its first attack on the 
host often begins with an indentation in it, as was described above in page 364 in the 
case of the penetration of many germ-tubes. In some cases, as in the club-shaped 
haustoria of Peronospora densa*, the indentation is all that is effected; further 
investigation of these matters which have hitherto been little regarded may bring to 
light other instances of the same kind. 
Lastly there are endophytes, whose hyphae do not pierce through the membranes, 
but grow in them in the direction of their surface and there ramify. Some species of 
Exoascus, according to Sadebeck’s observations noticed above on page 265, spread 
in this way all their life long in the outer wall of the epidermis beneath the cuticle of 
the parts attacked, which they do not burst through till they form their asci. Other 
species, like Exoascus Pruni, behave in a similar way, only their mycelium grows through 
the inner tissue into the subcuticular wall, taking its way as is usually said ‘ between 
the cells;’ but it would be more correct and more in accordance with known facts 
to say in the cell-membranes. The mycelium of Rhytisma Andromedae, which forms 
sporocarps, spreads beneath the cuticle in the outer wall of the epidermis in the 
same way as that of Exoascus; the mycelia which produce spermogonia of Puccinia 
Anemones, of Phragmidium and of some other Uredineae, and, according to Cornu ‘¢, 
the mycelium of Cladosporium dendriticum in the fruits of the Pomaceae, pursue a 
similar course. These Fungi burst through the cuticle and come to the surface when 
they form their spores or spermogonia. The path of the Fungus must really be 
intercellular to reach this position in the Uredineae ; how it arrives there in other 
cases is not known. In the Fungus which lives in the vine and which I named 
Sphaceloma ampelinum, the germ-tubes of the gonidia penetrate into the outer wall 
of the epidermis and spread in it beneath the cuticle, which is only burst by the 
small tufts of hyphae which grow up vertically to the surface and abjoint fresh gonidia. 

* Cited on page 160. 
? See R. Wolff, and Fischer v. Waldheim as cited on page 185. 
> Ann. d. sc. nat. ser. 4. XX, p. 29. 
* Comptes rend. 93 (1881), p. 1162. 
