22 Transactions British Mycological Society. 



Hypertrophy is a very frequent result of fungoid attack. 

 There is a great increase in cells, and these revert to more 

 primitive forms of tissue. Galls arise and there is abnormal 

 development of leaves and shoots. Perhaps the most 

 familiar and striking examples are the Witches' Brooms due 

 to Exoascus. 



Deformations and galls are also caused by the parasitism 

 of certain Uredineas, cases of which were investigated by 

 Ruth Stampfli,* She found galls might arise on stems, 

 leaf-stalks or leaves, in the latter, usually on the veins. 

 The palisade parenchyma is most influenced ; epidermal cells 

 and spongy parenchyma are altered in character, but do not 

 take much part in gall formation. Leaf-stalks and stem 

 galls arise through the activity of similar tissues, chiefly 

 through the enlargement and increase of the pith, of the 

 woody tissues, and of the cambium, and to a lesser degree 

 of the cortex, phloem and epidermis. She found that usually 

 there is a tendency for the tissues to revert to the more 

 simple parenchyma structure; the thickening of cell-mem- 

 branes both in wood and in bast fibres is less complete, 

 while the cortex, pith, and other parenchymatous tissues are 

 distinctly more developed. 



fWakker also has placed on record the changes induced 

 in the host by various parasites. He finds in all true cases 

 of hypertrophy an enlargement of the host cells with conse- 

 quent obliteration of the intercellular spaces, as also certain 

 alterations in the contents of the cell such as colouration of 

 the cell-sap, the formation or the disappearance of crystals 

 and the transitory accumulation of starch grains. There is 

 also a formation in some cases of new tissues such as in 

 the vascular bundles of Crucijerce attacked by Pcronospora, 

 in the meristem in the overgrown cells of ]^iola odorata and of 

 Zea Mays under the influence of Lhtilago, and the excep- 

 tional sclerenchyma formation in the stem of Cirsium 

 arvense, following infection b}- Puccinia suaveolens. In 

 other instances there is a disappearance of tissues as, for 

 instance, of interfascicular cambium in the host plants of 

 Cystopus candidus, and more or less of the cambium, phloem 

 and secondary wood in Rhamniis, due to the presence of an 

 ^cidium. 



In Exobasidium on Vaccinium, Sjc, the leaf-blister is due 

 to the enlargement of the parenchyma cells, which also be- 

 come more rounded and of simpler form, a reversion to a 

 more primitive type of structure, while specialized tissues, 



* Stiimpfli, 'q-'io. t Wakker, '92. 



