62 



STIMULATIVE INFLUENCES. 



plants consist of an ethereal combination of cellulose with a 

 substance to which he gives the name liadromal. The dissocia- 

 tion of this compound and the liberation of cellulose, are 

 probably effected by an enzyme which this worker has dis- 

 covered in certain fungi, e.g. dry-rot (§ 80), and which he terms 

 hadromase. Fungi that have invaded trees and timber find, in 

 the bark and cambium layer of same, oftentimes large amounts 

 of glucosides, such as salicin, populin, amygdalin, coniferin, &c. 

 Thanks to the action of certain excreted enzymes, such as 

 emulsin, they are able to utilise for their own nutrition the 

 carbohydrates separable from these substances. A number of 

 these parasites were examined in this I'espect, with affirmative 

 results, by E. Bourquelot (III. and IV.). Further mention of 

 Eumycetes enzymes capable of decomposing glucosides will be 

 made, with reference to certain special examples, in a later 

 section. 



. However useful to parasites may be the faculty of secreting 

 an enzyme capable of dissolving the cell walls of the infested 



host, there are certain cases 

 where the parasites can dis- 

 pense with this faculty and 

 still attain the end in view. 

 This is effected by the 

 purely mechanical pressure 

 exerted by the apex of the 

 hypha on the cell wall of 

 the host, when the hypha 

 itself has formed an appres- 

 sorium (§ 237) and thus pro- 

 vided an abutment. In this 

 manner it succeeds in per- 

 forating the cell wall. This 

 faculty has been confirmed 

 by M. MiYOSHi (II) in the 

 case of Penicillium glaucum 

 and Botrytls cinerea, both of which proved capable of penetrating 

 thin gold leaf quite free from holes. In this case chemical action 

 was entirely precluded. When fungoid hyphse obtain a footing 

 on the epidermis of such parts of plants as exhibit stomata, they 

 often prefer to obey the chemotropic attraction exercised by the 

 cell contents, in a peculiar manner, by growing towards the 

 nearest stoma, passing, by this means, into the interior of the 

 plant tissue, and then penetrating the cell membranes, which 

 are far thiniier than that of the epidermis. An example of this 

 is shown in Fig. no. The successful entrance of the hyphai in 

 this manner is not, however, invariably followed by the further 

 development of the parasite, the sequel depending on the con- 

 stitution of the cell contents. The latter, without prejudice 



Fig. 1 10. — Khizopus nigricans. 



Hyphfe from Ave spores, which, twenty- 

 seven hours previously, were sown on tlie under 

 surface of a leaf of Ti-adescantia dincolur that 

 had been injected witli a 2 per cent, solution of 

 ammonium chloride, making their way to the 

 stoma, and passing there through into tlie in- 

 terior of the leaf tissue. Magn. 100. {After 

 Miyoshl.) I 



