362 DIVISION III. MODE OF LIFE OF THE FUNGI. 



towards it, enters it and developes into a mycelium. If germination, which occurs 

 readily everywhere in a damp atmosphere, takes place on some other substance, the 

 tubes grow irregularly in every direction and perish after a short increase in length. 

 The entry through the stomata has been observed also in species of Entyloma 1 and 

 Kuhn's Polydesmus exitiosus 2 . Further instances will be found in pathological 

 literature. 



Among endophytic parasites on animals I mention here the germ-tubes of the 

 aerial gonidia of Cordyceps militaris (' Isaria farinosa '), which I only saw enter the 

 stigmata of caterpillars on which they had developed from the germinating spores 3 ; 

 but this observation requires to be revised. 



The second case in which the germ-tubes or hyphae pierce through the firm 

 membranes of the uninjured host is probably the more common. It is of course the 

 form which occurs in all endophytes on unicellular organisms. Examples of it are 

 seen in the case of parasites on higher plants in the germ-tubes from the sporidia of 

 the Uredineae, excepting always Leptopuccinia Dianthi just mentioned, and in those 

 of most of the Peronosporeae and Ustilagineae 4 ; Polystigma rubrum 5 together with 

 many other Pyrenomycetes and Discomycetes, Claviceps also and the facultatively 

 parasitic Sclerotinieae (see section CVIII) may be added to the list. It is to be 

 particularly observed that the germ-tubes of these parasites on higher plants never 

 penetrate into the host by a stoma. Even if the spore lies on or near a stoma, the 

 germ-tube either pierces through a guard-cell, or crosses the cleft as it grows and 

 pierces the wall of an adjacent cell. 



The germ-tubes of most of the insect-killing Cordyceps, Botrytis Bassii, and the 

 Entomophthoreae belong to this class ; their tubes pierce through the chitinous skin 

 of the body of the host, and may begin to ramify in the substance of the thick 

 chitinous skin of the larger caterpillars. 



Some parasites on plants show both modes of proceeding, for the same germ- 

 tubes may penetrate through the stomata and through the membrane of epidermal 

 cells ; this is the case in Peronospora parasitica, Phytophthora infestans, and Exoba- 

 sidium Vaccinii 6 ; species also of the mode of life of Sclerotinieae can enter the host 

 by the stomata. 



Finally, there are a certain number of parasites whose germ-tubes and hyphae 

 penetrate into woody plants, not through uninjured surfaces, but where some wound 

 has been received, and from thence make their way into open spaces, such as injured 

 vessels (Nectria cinnabarina), or pierce through the cell-membranes. This is the case 

 with most of the tree-destroying Hymenomycetes studied by Hartig, with Peziza Will- 

 kommii and the species of Nectria which are parasites on trees. See section CVIII. 



From this series of phenomena which constitutes the general rule deviations occur 

 in two directions, but the deviations are connected with the rule by intermediate forms. 



One of these deviations is found chiefly in endophytes which vegetate intracellu- 



1 Bot. Ztg. 1874, pp. 93, 103. 



9 Krankheiten d. Culturgewachse, p. 152. 



3 Bot. Ztg. 1869, p. 590. 



' Wolff, as cited on page 185. Kiihri, in Sitzgbr. d. Naturf. Ges. Halle, 24 Jan. 1876. 



1 Fisch, in Bot. Ztg. 1882, p. 851. 



* Woronin. as cited on page 341. 



