Ward. — Recent Researches on the Parasitism of Fungi . 29 
many parasitic spores, only capable of attacking young organs, adopt this 
mode of cuticular infection. 
In the case of uredospores and aecidiospores the process is different, 
as De Bary first showed ; their germ-tubes enter the stomata, and it is with 
this stomatal infection only that we have here to do. 
But further research shows that two events must be sharply distin- 
guished, in addition to the preliminary act of germination of the spore itself 
First, we have the entry of the germ-tube via the stoma, preceded by 
a swelling of the tip into the so-called appressorium over the external 
orifice of the stoma. The tip then sends a slender offset through the orifice 
into the respiratory cavity, and there it swells into the siib-stomatal vesicle , 
and the entry of the Fungus is assured. 
Secondly, we find this sub-stomatal vesicle puts forth one hypha (or 
more) which grows towards the cells bounding the inter-cellular spaces? 
attacks them by sending in haustoria, and thus the act of infection is 
completed. 
It will be evident that we have in the process of entry or inoculation , 
a phenomenon quite distinct from and independent of that of infection. 
We cannot assume that either the stomatal or the mesophyll-cells of 
the host are passive or inert in this matter. As regards the former it is 
suggestive that inoculation is best effected by sowing in the evening ; it 
often fails in bright daylight, and apparently always does so if the tempera- 
ture is high, or the plant in darkness. 
In 1882, at Owens College, I observed the following phenomenon. A 
slice of bean-stem in a hanging drop, to which some zoospores of a Pythium 
were added, was under observation. A zoospore was seen to gyrate rapidly 
in smaller and smaller circles, and suddenly dart on to the exposed cut 
surface of the bean section, where it remained stationary, and in half an 
hour had begun to germinate. In a couple of hours its tip was boring 
through the cell-wall. 
My attention at the time was directed to other matters ; and it is to this 
fact and to my lack of that particular form of insight which is called genius 
that must be ascribed the stupid failure to see that here was a case of 
what we now know as chemotaxis. 
In 1883 ( 128 , p. 524) Pfeffer published his first paper on the 
directive actions of chemical stimuli, which he subsequently named 
chemotaxis, and which he showed to be so potent a factor in attracting 
the tips of hyphae to enter plants ; a theme worked out more in detail in 
this connexion by his pupil Miyoshi ( 113 ), 1894, and ( 112 ), 1895. 
I have always maintained that in parasitism we must consider not 
only the power of the parasitic Fungus to attack a given host-plant, but also 
the reaction of the host on the parasite ( 198 ), 1890, and ( 197 ), and also ( 190 ), 
and it is characteristic of modern work that this view is spreading. 
