EFFECTS OF PARASITIC FUNGI ON TISSUES OF HOST. 41 



simple galls of this kind are cells of Pilohnhis Klcinii inhabited 

 by Pleotrachelus fulgens, cells of turnip infested by Flasmodio- 

 phora, or of dandelion with Synchytrium. 



Cell-enlargement resulting from the influence of extracellular 

 parasites is most distinctly seen in those algal cells, which 

 form lichens with the hyphae of certain fungi. Thus according 

 to Stahl, the algal cells of the lichen Endocaiyon pusillum 

 Ijecome enlarged six-fold. 



Cell-enlargement accompanies all hypertrophy of plant organs, 

 whether the parasite lives purely intercellular, or has haustoria. 

 At the same time one generally finds a disappearance of the 

 intercellular spaces present in the normal tissues ; in some 

 special cases, however, these may become more numerous and 

 larger. Cell-enlargement, accompanied by disappearance of 

 normal intercellular spaces and chlorophyll, are shown by 

 Woronin's illustrations to be very marked in the galls on cow- 

 berry, due to Exohasidiiim vaccinii. Cell-enlargement is also 

 frequent in cases of hypertrophy due to Exoasceae ; thus in 

 Taphrina aurea, although the mycelium is only subcuticular 

 or penetrates but slightly into the epidermal layer, yet the 

 cells are much enlarged and their walls are strikingly thickened 

 (Fig. 63). Smith ^ found that when leaves became thickened 

 in consequence of attacks of certain species of Taphrina, their 

 cells became larger and rounder, so that the large intercellular 

 spaces of the spongy parenchyma disappeared and the char- 

 acteristic appearance of that tissue was lost. 



The epidermis, as has already been indicated, is influenced 

 by fungi which live between the cuticle and cell- wall, as well 

 as by epiphytic fungi, whose haustoria penetrate it. The 

 epidermis is, however, more frequently destroyed by endophytes, 

 which rupture it in forming their reproductive organs. Some 

 of tliese produce their sporocarps inside the epidermal cells, 

 and, as they enlarge, cause detachment of the outer walls of 

 the cells from the remainder, to form for a time a covering 

 which is ultimately ruptured as the sporocarps attain maturity. 

 Where the fungi live under the cuticle {e.g. the Exoasceae), 

 this alone is ruptured when the asci are formed. The repro- 



' William fi. Smith. " Untersuchiing d. Morphologic u. Anatomic d. (lurch 

 Exoasceen vcrursachten Deformatioiien. " Inaiig. Dissertation, Munich, 1894; 

 also, Forstiich-naturivisa. Zeit^chrift, 1894. 



