382 DIVISION III. MODE OF LIFE OF THE FUNGI. 



its cultivation, though they may supply unequal amounts of nutrient material. On the 

 other hand it by no means attacks every kind of Phanerogam as a parasite. I was 

 unable to find, after repeated and careful search, any trace of the Fungus on the plants 

 of a moist meadow close to the beans above mentioned. Among plants under cultiva- 

 tion one variety of Phaseolus vulgaris in the same garden was very slightly infected 

 with the Fungus in spite of the immediate proximity of the others. Experiments 

 in inoculation also showed that Phaseolus multiflorus was scarcely ever attacked ; in 

 other specimens the Fungus developed only scantily, but in single young seedlings kept 

 very moist its growth was vigorous. Living plants of Brassica (B. rapa, B. Napus, 

 and B. oleracea) were never attacked, either as young seedlings or as plants ready to 

 blossom. Further details must be reserved for another place. 



It should be added, that the hyphae of the Fungus when once they have become 

 capable of infecting make their way into the superficial living cells by piercing their 

 walls, and grow indiscriminately in and between and through the cells of the living 

 tissue and soon kill them. The power of infecting is shown by the power of penetrating 

 the membranes, which are evidently dissolved at the points of penetration. Hence it 

 is very probable that this power depends on the presence of a substance which can 

 dissolve a membrane, a ferment in fact, and that this substance is not formed and 

 discharged in sufficient quantity till the germ-tube from the spore is properly nourished 

 and developed. 



The foregoing statements with regard to the power possessed by Sclerotinia Sclerotiorum 

 of infecting are in opposition to some which have been published in other works and 

 especially in Frank's Pflanzenpathologie, p. 530 ff. ; according to these accounts the young 

 germ-tube has the infecting power without previous preparation, and plants of Brassica 

 were at once attacked by the Fungus. The observations may be correct in both cases 

 and the difference may arise from the fact, that several species resembling one another 

 in appearance, but differing in the mode of vegetation, are confounded together under 

 the name of Sclerotinia Sclerotiorum. The discussion of this point would occupy us 

 too long and must be reserved for another occasion. 



Among other species of Pythium 1 which have been carefully examined Hesse's P. 

 de Baryanum is a parasite on living and healthy plants, and attacks them both with 

 its germ-tubes which are formed in water and with the branches of the mycelium 

 when it has acquired strength. It attains its full development equally well on dead 

 vegetable substances and on the dead bodies of animals, and is therefore equally a 

 saprophyte and a parasite. In the latter character it penetrates into the cells of a 

 great variety of Dicotyledons and Monocotyledons and into the prothallia of Ferns, 

 but leaves plants of Spirogyra and Vaucheria untouched. Some Phanerogams are 

 also said to be secure from its assaults, but this statement requires confirmation. It 

 attacks with especial readiness and frequency the young and watery seedlings of 

 Phanerogams such as the Cruciferae and Amarantus, taking possession of them and 

 destroying them rapidly and completely. Full-grown land-plants are usually less readily 

 attacked and the injury done to them is more local; but they too may be rapidly 

 destroyed by the Fungus if they are placed in water. 



Other and nearly allied species of Pythium are, as far as is known, partly pure 

 saprophytes, partly facultative parasites within narrow limits. P. intermedium and 

 P. megalacanthum grow as saprophytes on dead parts of plants. They leave living 

 Phanerogams, even young seedlings which are so liable to the attacks of P. de Bary- 

 anum, always and absolutely untouched ; but P. intermedium readily attacks the 



Bot. Ztg. 1881, p. 531. 



