392 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in diameter ; and at the time when tliey are formed the hyphae are 

 found to contain large quantities of starch, which is partly used up 

 in the formation of their cellulose-wall, and which is no doubt derived 

 from the oil that is present at an earlier stage ; the spores themselves 

 do not contain starch. Portions of the hyphae remain colourless, and 

 in these no spores are formed. 



Although Phyllosiphon is found only in the intercellular spaces of 

 the leaf and leaf-stalk of the host, the protoplasmic contents of the 

 neighbouring parenchymatous cells undoubtedly supply it with 

 nutriment, and it must be regarded as a true parasite. The inter- 

 cellular spaces become in time entirely occupied by it, so that the 

 respiration of the host must be greatly impeded. 



As soon as the spores are completely formed in a portion of a 

 branch, they escape spontaneously, the expulsion being caused by the 

 great capacity for swelling possessed by the central portion of the 

 protoplasm, the parietal layer at the same time contracting, and being 

 ruptured in consequence. There is always, however, a certain pro- 

 portion of the spores left behind in the hypha, surrounded by a portion 

 of the protoplasm, and connected with one another by fine bands of 

 protoplasm. The portions of the hypha which burst are frequently 

 immediately beneath stomata, through which the spores are forced. 

 This takes place chiefly on the under side of the leaf, the hyphae 

 forcing themselves only rarely and with difficulty between the com- 

 paratively closely packed palisade-cells which lie beneath the epi- 

 dermis of the upper sui-face. The expulsion is effected with great 

 energy, the spores being forced on to the external surface of the leaf. 

 Those which remain in the hyphae continue to grow, some of them 

 attaining the size of 8 jx diameter and more ; while others remain about 

 the size of the expelled spores. 



That the green colouring-matter of Phyllosiphon, although not 

 occurring in the form of distinct grains, is chlorophyll, is beyond 

 doubt ; an alcoholic solution shows all the characteristic spectroscopic 

 properties of this substance. It appears certain that this chlorophyll 

 is not derived directly from that in the leaf-cells of the host ; but 

 that it is formed by the organism itself. Its purpose appears to be 

 not to decompose carbonic acid in the hyphae, but to jDass entirely into 

 the spores, which carry on an independent development outside the 

 host, and require the chlorophyll for this purpose. 



All attempts at artificial germination of the spores failed, both of 

 those that are expelled, and of those, whether larger or smaller, that 

 remain in the hyphae ; as also did similar experiments with the hyphas 

 themselves. The reason of this failure is no doubt that the spores 

 require to go through a period of rest before germinating. In nature 

 this period of rest extends from the middle of March, when the 

 patches are most abundant (no fresh ones being formed after the 

 middle of April) till December, when they begin to appear again. 



Until the complete life-history of Phyllosiphon has been followed 

 out, its systematic position must remain in uncertainty. Schmitz's 

 view, that it belongs to the Phycomycetes, must be entirely abandoned ; 

 nor does the mode of formation of the spores justify us in placing it. 



