150 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fungi. 



By A. LoRBAiN Smith, F.L.S. 



Culture Experiments with Rhizopus nigricans.* — ^Arthur H. 

 Graves has been investigating the behaviour of fungal hyphffi in 

 relation to chemotropic stimuli. He selected the above fungus (along 

 with some others) and watched the growth of the hyphse very exactly. 

 Perforated mica plates were employed, separated by two layers of 

 medium, and various combinations of spores and chemical substances in 

 these two layers were experimented with. 



He summarizes his results thus : Many fungi exhibit a negative 

 chemotropism toward their own metabolic products (staling substances). 

 Positive chemotropism towards such substances as turnip-juice, cane 

 sugar and glucose was also observed. The substances in turnip-jaice 

 exert a stronger positive chemotropic effect than, e.g. 10 p.c. cane sugar. 

 Finally it is surmised that the distribution of a parasitic fungus in its 

 host is due not so much to positive chemotropic stimuli as to the 

 dominant chemotropism towards its own staling products. 



Pythiacystis on Avocado Trees in California. f— Howard S. 

 Fawcett has investigated a disease of these trees which was characterized 

 by the exudation of gum, and, in addition, by the deposit on the surface 

 of the injured area of a white powdery crystalline substance. The 

 trouble occurs not only on large trees, but also on small seedlings, 

 especially if they have been over-watered. Culture experiments were 

 made in tubes in all of which a Pythiacystis (Saprolegniacese) was 

 developed ; and inoculation of healthy trees l)y mycelium from the 

 culture tubes reproduced the disease. 



Tarichium : a Genus of Entomophthorege.l — The fructification of 

 this genus is unknown. It includes a number of very uncertain forms, 

 and is in the nature of a collective or provisional genus. G. Lakon 

 gives a list of species that might be considered as true species, and of 

 others that do not belong to any genus of Entomophthorea;. He 

 discusses the economic value of these fungi as causing diseases of insects ; 

 occasionally they have proved of great service in reducing the insect 

 pest, but too little is as yet known of the biology of the group. 



Development of the Perithecium.§— M. F. Vincens has made a 

 special study of this subject, and he publishes the details of growth and 

 development of a somewhat peculiar character in a 3Ielmiospora, one of 

 the Hypocreacea3. The ascogonium consisted of a globose cell borne on a 

 stalk one to two septate. It is multinucleate, as are most of the cells of 

 the thallus. From the stalks issue short branches which cluster round 

 the ascogonium and form an inner wall, one-cell thick. Spiral cells 



* Memoirs New York Bot. Gard., vi. (1916) pp. 323-31. 

 t Phytopathology, vi. (1916) pp. 433-5. 



J Zeitschr. Pflanzenkr., xxv. (1915) pp. 257-72. See also Bot. Centralbl.. 

 cxxxi. (1916) p. 621. 



§ Comptes Eendus, olxiii. (1916) pp. 572-5. 



