CHAPTER VIT.—PHENOMENA OF VEGETATION.—PARASITES. 365 
In some endophytes, Phytophthora omnivora', Tuburcinia Trientalis*, Proto- 
myces macrosporus*, the entrance of the germ-tube of the parasite into the cells of 
the host is more narrowly localised within the limits assigned above. While most 
perforating endophytes make their way into the interior of the cells of the host at any 
spot on their outer surface, the three Fungi above named make their entrance at the 
outer edge of the side wall which divides two epidermal cells, and then grow on in 
the middle lamella of this wall, splitting it in two and so pressing transversely or obliquely 
through the epidermis; ultimately they produce both an intracellular and an 
intercellular mycelium. This is at least the prevailing mode of penetration in these 
species; perforation of the outer wall and lumen of an epidermal cell occurs 
exceptionally in Phytophthora. 
“In some of the purely epiphytic Fungi which do not penetrate into the host, 
some for example of the Chytridieae* and the Laboulbenieae, the spores when 
conveyed by some method of dissemination adhere simply to the surface of the host, 
which is large in comparison to the parasite. The Lichen-fungi which live on small 
and usually unicellular Algae put out germ-tubes which embrace the cells of the host, 
as will be described in section CXV, when they encounter them in their elongation. 
It has never been observed that the direction of this growth is influenced by the host 
before contact. 
Kihlman 5 has recently observed a very remarkable arrangement for fastening on 
the host in the case of Melanospora parasitica, which is epiphytic on species of Isaria. 
The almost cylindrical brown-walled spore, which is 5-6 a in length, germinates by 
the emission of a germ-tube at each extremity, the tubes, whether grown in water or 
in nutrient solutions, being scarcely longer than the transverse diameter of the spore. 
If the spore lies against or on a hypha of Isaria, which is most frequently the case in 
a state of nature, the germ-tube becomes firmly attached to the hypha of the host and 
then developes into a mycelium. If the germ-tube comes into contact with an older 
hypha of Melanospora, the membrane which separates them is dissolved and they 
coalesce with one another. But if a germinating spore lies at some distance from a 
growing hypha of Isaria, and it is not difficult to procure this in plants grown 
on a microscopic slide, the direction of its growth in length is deflected towards 
the spore till it comes in contact with the germ-tube, which then unites with it 
and begins to develope. The greatest distance at which the germinating spore can 
influence the direction of growth of the hypha is from four to five times the length of 
the spore. , 
The physiological analysis and explanation of all these phenomena of 
aggression, adhesion, and penetration through openings and membranes has yet to be 
undertaken. We can here only notice briefly some of the chief points to be 
considered. 
The facts which have been stated above with regard to the perforation show, on 
the one hand, distinct effects produced by the germ of the parasite on the host. The 

U R. Hartig, Arbeiten d. forstbot. Instit. München, I. 
? Woronin, as cited on page 185. 
® Wolff in Bot. Ztg. 1874. 
* See above, p. 171. 
5 As cited on page 262. 
