ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 507 



Fungi. 

 (By A. Lorrain Smith, F.L.S.) 



Homothallic Conjugation in Rhizopus nigricans.* — Florence A. 

 McCormick records an undoubted case of conjugation between two 

 closely approximate parts of the same hypha. The material was grown 

 from spores on bread moistened with a solution of grape-sugar. Blakeslee 

 had already admitted the possibility that a homothallic race may occur 

 in a normally heterothallic species, such as Rhizopus nigricans. 



Norwegian Mucorini. II. f — 0. Hagem published his first paper on 

 the Mncors of the soil in 1907. He now gives the results of culture 

 experiments to test nutrition and growth conditions. The behaviour of 

 these moulds in these respects differs in the various species. About 

 thirty species in all have been isolated from the soil ; the differences 

 found to exist among them, as to the substances on which they can live, 

 are described, but, in general, the author found that fungi are obliged 

 to reduce all nitrogen compounds into ammonia before they can utilize 

 them as nutriment. 



These soil fungi are harmful, so far as they withdraw ammoniacal 

 salts from the soil, changing them into fungal albumen ; they are 

 beneficial in decomposing the nitrogen compounds of decaying vegetation 

 and in transforming them into ammoniacal compounds. 



Infection of the Vine by Plasmopara viticola.^: — II. Muller-Thiirgau 

 has carried out a series of infection experiments on vine-leaves to study 

 the methods by which the fake mildew fungus spreads so rapidly. The 

 longer the time given, the more infections were found on the leaves, 

 which were kept in a damp chamber. Very rarely were any spores found 

 to have pierced the upper epidermis ; usually infection took place by the 

 stomata of the under surface ; if, however, the epidermis was scratched 

 or wounded, the spores germinated and entered the leaf at the injured 

 spot. The best results were obtained with young leaves. Even when 

 older leaves were infected, the fungus failed to grow with vigour, and 

 only a few conidiophores were formed. 



Experiments with Phytophthora.§ — G. H. Pethybridge has made 

 a series of experiments to test the theory that potato-blight is kept alive 

 and spread by means of dormant mycelium in the tuber. Among other 

 experiments, he planted thirty-two diseased tubers, and though many of 

 them rotted in the ground fifty-three plants developed, not quite so robust 

 as those grown from healthy tubers, but perfectly free from the fungus. 

 Later they were attacked by the disease in the ordinary fashion from 

 wind-borne spores, the outstanding leaflets being first infected, the stalks 

 meanwhile remaining free from the fungus. He concludes that there is 

 no evidence at present to show that the disease is caused otherwise than 

 by aerial spores. Diseased tubers left exposed might very well produce a 

 crop of spores which would easily give rise to an epidemic of Phytophthora. 



* Bot. Gaz., li. (1911) pp. 229-30 (1 fig.). 



t Vid.-Selsk. Skr. I. Math. -Nat. Kl., iv. (1910) 152 pp. See also Bot. Cen- 

 tralis., cxvi. (1911) pp. 256-7. 



% Centralbl. Bakt.,xxix. (1911) pp. 683-95 (fig.). 

 § Sci. Proc. Roy. Dublin Soc, xiii. (1911) pp. 12-27. 



