ZOOLOGY AND BOTANY. MICROSCOPY, ETC. 415 



Comparative studies were made with Azotobacter, and the usual gain of 

 nitrogen appeared in the cultures. 



A second contribution * reports the results of an experimental study 

 on the wood-destroying fungus Lenzites ssepiaria, with special reference to 

 enzyme production and action. • Most of these are formed in the 

 vegetative mycelium, though oxidases are more active in the sporophores. 



Chemotropic Reactions in Rhizopus nig^ricans.t — Arthur H. Graves 

 gives a contribution to our knowledge of the behaviour of fungal hyphfe 

 m relation to chemotropic stimuli. The fungi experimented with were 

 Rhizopus nigricans, Botrytis cinerea and Penicillium, and perforated mica 

 plates were used in the cultures. Graves found that the fungi exhibited 

 a negative chemotropism toward their own metabolic products (staling 

 products), and the negative influence was much stronger than the 

 positive influence of culture media, such as turnip-juice, cane-sugar and 

 glucose. " The distribution of parasitic fungi in the host-plant is there- 

 fore probably due, not so much to positive chemotropic stimuli, as to 

 the dominant negative chemotropism towards their own staling products." 



Plant Diseases. J: — F. L. Stevens has given a list of Porto Rican 

 plant diseases, of economic importance, with short notes. Among the 

 most interesting are Hemileia vastatrix, which appeared on coffee, but 

 was recognized and immediately stamped out. Another disease of coffee, 

 Pellicidaria hohroga allied to Hypochnvs, is prevalent and very destruc- 

 tive ; it attacks the leaves. Various forms of black moulds occur on 

 leaves : — Meliola on palm, on orange, on mango, and on guava. Uredinete 

 such as Graphiola Plmnicis 5n palms ; Uredo Artocarpii on bread-fruit ; 

 Uromyces on pea-nut, gondule and manihot ; Kuehneola Gossypii on 

 Ficus and cotton ; and Coleosporium on sweet-potato. 



" Leaf Spot," § or blight of celery (Septoria Apii), has been greatly on 

 the increase in recent years. The disease attacks the outer leaves first, 

 and they become discoloured and finally rot away. On the discoloured 

 areas may be seen the minute perithecia that are the fruits of the fungus. 

 The fruits of the celery may also be diseased, so care is advisable in 

 choosing clean seed, and all diseased plants should be carefully burned. 



Sharpies || has shown the role played by insects in spreading the 

 collar rot of rubber-trees {Hevm hrasiliensis). The disease is due to the 

 fungus Ustulina zonata, and it has been found that a plantation is often 

 attacked at the time of thinning operations when the trees are about six 

 or seven years old. The trees that are left are often wounded on the 

 bark, accidentally abraded by others falling against them, and so the 

 attack of boring beetles {XyUhorus parvulus) is facilitated and becomes 

 very common. The fungus follows in the tracks of the beetles, these 

 providing a ready entrance for the mycelium. It is also pointed out 



* Ann. Miss. Bot. Gard. iii. (1916) pp. 439-509. 

 t Mem. N.Y. Bot. Gard., vi. (1916) pp. 323-31. 

 t Phytopathology, vii. (1917) pp. 131-4. 

 § .Tourn. Board Agric, xxiv. (1917) pp. 68-70 (1 pL). 



II Dept. Agric. Fed. Mai. Stat., Bull. 25 (1916). See also Nature, xcviii. (1917) 

 p. 500. 



