ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 87 



distribution, and of experiments to test the vitality of the spores. 

 The thermal death-point of Phoma on leaves exposed to dry-heat for 

 half-an-hour was 80° to 90° C. It dies after three months' storage in 

 soil. It does not sarvive the process of ensiling the beet-tops. 



H. A. Edison * has also studied Phoma Betse from a histological point 

 of view. The period that the host is susceptible to infection is the 

 seedling stage. The cells of the plant attacked were often nearly 

 filled with the fungus, and it seems probable that though the middle 

 lamella is dissolved the parasite does not live on it. Heavily invaded 

 cells are consumed ; the cytoplasm disappears, and the nuclei dis- 

 integrate. There may exist also less virulent infections, in which, 

 though the fungus is established i in the tissues, the beet continues a 

 healthy growth ; the balance is, however, not a healthy one, and in 

 storage the activity of the parasite may be renewed. 



A root-rot of Ginseng has been determined by J. Rosenbaum f as 

 due to the Hyphomycete Alternaria panax ; it results in yellowing and 

 wilting of the leaves. Cultures and inoculations were made. 



As a result of cultural and morphological studies, J. Rosenbaum % 

 has established the pathenogenicity of a Sderotinia causing the white- 

 rot of Ginseng, and he has proved its identity with S. libertiana, which 

 occurs on lettuce, celery, and a number of other hosts. He has also 

 studied the Sderotinia that causes black-rot of Ginseng, and finds it 

 identical with S. SmUacina. 



W. D. Valleau § has studied the resistance of plums to brown- 

 rot, Sderotinia cijierea. Infection may take place at any time through 

 the skin, but different varieties have different powers of resistance 

 after infection, due to parenchymatous plugs of the stomatal cavity, the 

 production of corky walls, etc., rather than to any peculiar content of 

 the fruit. Brown-rot is essentially a rot of ripe plums, at the stage 

 when the fruits are softening. The hyphaj are intercellular, but do 

 not dissolve the middle lamella. It was not possible to extract an 

 enzyme from the fungus. The internal hyphas lend support to the 

 plums, hence it is a firm rot and the plums mummify. PenicilUum 

 expansum, on the contrary, produces a soft rot by dissolving the middle 

 lamella. 



Die-back of apple-trees has been traced to the fungus Cytospora 

 leucostoma by Van der Byl.|| It also occurs on other fruit-trees of the 

 Rosaceae. It begins as a brownish-black coloration near the soil and 

 spreads upwards. Diseased trees usually die the second summer after 

 attack. Species of Cytospora have been determined as the pycnidiat . 

 stage of Valsa, but the writer was unable to produce any higher fruiting 

 form in his cultures. He gives a detailed description of the disease and 

 suggests methods of cure. 



A disease of Sweet-Potato known as scurf was studied by Halstead If 



* Journ. Agric. Research, v. (1915) pp. 55-7 (2 pis.), 

 t Journ. Agric. Research, v. (1915) pp. 181-2 (2 pis.). 

 i Journ. Agric, Research, v. (1915) pp. 291-7 (2 pis. and 1 fig.). 

 § Journ. Agric. Research, v. (1915) pp. 365-95 (3 pis.). 

 11 African Journ. Sci., xvi. (1915) pp. 545-57 (4 pis. and 4 figs.). 

 ^ Journ. Agric. Research, v. (1916) pp. 787-91 (2 pis.). 



