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 2 . 



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. 



1 Cited on page 160. 



2 See R. Wolff, and Fischer v. Waldheim as cited on page 185. 



3 Ann. d sc. nat. ser. 4. XX, p. 29. 



4 Comptes rend. 93 (1881), p. 1162. 



