240 HOST PENETRATION 



Penetration by infection hvphae of the same type is known 

 among other pathogenic fungi. Blackman and Welsford (1916) 

 noted that Botrytis cinerea pierces the cuticle of Vic'ia faba by 

 mechanical pressure exerted on a narrow outgrowth from the 

 germ tube. Waterhouse (1921) recorded the occurrence of a 

 mucilaginous envelope on the germ tubes of sporidia of Puccinia 

 graminis germinating on leaves of Berberis vulgaris. The muci- 

 laginous matrix fixed the sporidium and germ tube to the leaf. 

 Penetration of the cuticle was accomplished by mechanical pres- 

 sure exerted upon a beak-like outgrowth from beneath the spo- 

 ridium or upon a very tenuous style-like hypha beneath the germ 

 tube. After penetration the tip of the infection tube swells into 

 a vesicle, and from it the mycelium forms. 



Penetration by boring through the host-cell membranes has 

 been observed and described in several Phycomycetous species. 

 Curtis (1921) noted entrance of zoospores that had come to rest 

 and of young zygotes of Synchytrhnn endobiotiaim into potato 

 tissues. A small protuberance develops on the side in contact 

 with the host, which eventually perforates the wall. The tip of 

 the tube then enlarges into a vesicle within the lumen of the host 

 cell, into which the entire protoplast flows, leaving the empty 

 wall of the resting cell or of the zygote outside the host. Similarly 

 Tisdale (1919) noted migration of the content of erstwhile zoo- 

 spores of Phy so derma zeae-may dis through narrow bore tubes 

 into the epidermal cells of corn. Among certain higher Phy- 

 comycetes, such as Peronospora tabacina, entrance may be effected 

 with apparently equal facility either by direct penetration or by 

 entrance through stomata. 



Among hyperparasites the hvphae of the one species may pene- 

 trate the walls of a second and grow within them, and others 

 merely entwine themselves closely around the host species. An 

 unusual type of hyperparasite and of direct penetration is pre- 

 sented in Parasitella (M/tcor) parasiticus and in Chaetocladium, 

 both of which are parasitic upon other Alucoraceae. Burgeff 

 ( 1924) described this relationship, pointing out that the sequence 

 of events is as follows: The hypha tip of the parasitic species, 

 after contact with the host hypha, cuts off a buffer cell. The 

 wall between this buffer cell and the host is then dissolved, effect- 

 ing a direct connection between them. The buffer cell then 

 enlarges, and hypha branches are developed from it. Meanwhile 



