EFFECT OF PARASITIC FUNGI OX THEIR HosT. 15 



cell attacked which is at once killed before it can enlarge or. 

 otherwise react to the influence of the intruder. Good examples 

 of such parasites are presented by some of the rhytridiac,-ae 

 -the Ai-rJt<'nii/i;f<.x of Fischer which, as a rule, inhabit only 

 isolated cells of their respective host-plants. This mode of 

 nutrition is equivalent tn that of the Myxomycetes and Mycetozoa, 

 which absorb the cell-contents after completely enveloping i la- 

 living cell, or after slipping inside or sendin- a haustorial pruc. 

 into it. 



A second series of parasites consists of those which live 

 on the contents of the host-cell, and give it time to react to 

 the stimulus exerted by the intruder. The reaction generally 

 results in a cell-enlargement or fungus-gall, which in the simpler 

 cases includes one cell only. The gall harbours one or more 

 parasites, which gradually use up the cell-contents. As examples 

 we have Utjiii/ittni tumaefaciens and 0. uredinis? /v^/W^/W ////// 

 saprolegnioe, o//m//>Y^-/.s saprolegniae, JU* /://///<" hypogaea* etc. 

 A specially striking case is that of Pleotrachdus fulgens, which 

 causes the rudiment of the sporangiophore of rilhuln* A'/'inii 

 to become hypertrophied and gall-like. 3 



We have as a third series those parasites which penetrate 

 into living cells and absorb their contents, at the same time 

 stimulating the bust-cell to abnormal and increased growth, as 

 well as some surroundinu cells not directly in contact \\ith the 

 fun-us. In this case the parasite exerts a tar-reaching effi 

 and produces a gall composi-d of more than one cell. Species of 

 Xi/,,rl,i/t,-iinii are examples. The fungus itself penetrates into one 

 cell only, which enlarges; but simultaneously the surrounding 

 cells -row and multiply to form a wall or rampart eiidosin- tin- 

 cell originally attacked. Other parasites do nut absorb the" 

 host-contents as a whole, but only withdraw osmotic substance- 



bv means of delicate processes of the fungus-hyphae. Tlh 



haustoi'ia j.enetrate tlie wall of the host-cell, but the fun-al 

 protoplasm inside them remains separated from the host-proto- 

 plasm by a delicate membrane. In the case of the vine-mildew 

 and some otber Krysipheae, the cells thus preyed on turn brown 

 and die. With otber related forms (..,/. N////-/. /<.///</ r,i</,i,/, 



1 S.M- | . I'll I/I-,, III I/I'' ' 



I in- i-.iu-i ^ a -hirlit -XM-llin^' i.t th<- font -li;iil - \ \.iliini.-, pliillts ami 

 I heir i-'iiiti-nl . 



/M|,I. Beitrdgt air /'A//-//. u, .\f"i-/>lnJ. ////. Organitmm, 11. I *>!'-'. 



