32 REACTION OF HOST TO PARASITIC ATTACK. 



effect of haustoria of Uredineae on the cell-nucleus. He describes 

 it thus : " The mycelium of Pucdnia asariina permeates between 

 the cells of the leaf-tissue of Asarum, and sends into almost 

 every cell of the infected part, a short, sometimes branched, 

 hypha, which serves as a haustorium. This grows in almost 

 every case towards the nucleus of the host-cell, and becomes 

 firmly attached thereto, or completely encloses it. The nucleus, 

 in consequence, undergoes considerable deformation, sometimes 

 being tightly constricted by the haustorium, or the apex of 

 the hypha penetrates deep into the nucleus, pushing the nuclear 

 membrane before it." 



Enlargement of the cell-nucleus occurs, according to Frank, 

 in the cells of the root-tubercles of Leguminosae caused by 

 bacteria; likewise in the cells of endotrophic mycorhiza of 

 orchids. Schlicht,^ in considering the endotrophic mycorhiza of 

 Paris quadrifolia, says, " One observes here, as in the mycorhiza 

 of the Orchideae, that the cell-nucleus, which is very large, can 

 exist in the cell beside the fungus-tissue. The hyphae, however, 

 frequently penetrate into the cell-nucleus, or surround it in 

 a close network."^ 



The effect of parasitic fungi on the chlorophyll of tissues 

 attacked by them is very varied. We may distinguish three 

 cases, apart from those in which the parasite kills the host-cell 

 and its chlorophyll along with it. In the first, the green parta 

 of the plant attacked become bleached by the influence of the 

 parasite, and ultimately lose their green colour; this we might 

 designate " mycetogenous chlorosis." Examples are the galls 

 of cowberry and species of rhododendron, the results of many 

 Uredineae, such as Chrysomyxa rhododendri on spruce, Aeddium 

 urticae on nettle, Oyninosporangium, clavariaeforme on hawthorn, 

 and the leaf-galls due to Exoasceae. 



In the second case, there is a preservation of the chlorophyll 

 in places infested by the fungus, in contrast to adjoining normal 



iSchlicht. "Beitrage z. Kenntniss d. Verbreitimg u. Bedeutung d. Mycorhizen.'' 

 Inaug. Diss. 1889, p. 14. 



^Groom (" Thismia Aseroe and its Mycorhiza," Annals of Botany, June, 

 1895, p. 339) describes and figures a similar case. He says, "The fungus 

 enters the cell as a single slender hypha, which at once grows directly towards 

 the nucleus of the host-cell." He also mentions an observation of R^fessor 

 Marshall Ward, "that in Hemileia of the coffee disease, the haustoria often apply 

 themselves to the nuclei of the host's cells." (Edit.). 



