AGRICULTUEAL BOTANY. 221 



search associates, the greater part of the work being conducted at the desert 

 laboratory near Tucson, Ariz. The investigations include further studies of 

 physical, chemical, and biological phenomena in connection with the Salton 

 Sea ; an analysis of the effect of climatic complexes and various external factors 

 upon plants; studies on photolysis, respiration, hydratation, and growth; and 

 various special investigations of Cactacese and other desert plants. 



Notes on the production of tropical plants, E. de Wildeman {Notes sicr des 

 Productions V^g^tales Tropicales. Antwerp: E. Stockmans <& Co., 1914, pp. 

 175). — Compiled and original notes are given on a number of economic tropical 

 plants, agricultural practices, plant diseases, etc., the substance of the several 

 articles having already been presented in various publications. 



Oblig'ate symbiosis in Calluna vulg'aris, M. C. Rayner (Ami. Bot. [London], 

 29 {1015), No. 113, pp. 97-133, pi. 1, figs. //).— This investigation was conducted 

 to determine the precise ecological conditions associated with small, well defined 

 communities of C. vulgaris in a restricted area of England. 



In common with other members of the family Encacete, C. vulgaris was 

 found to possess a characteristic root mycorrhiza. The infection by the 

 mycorrhizal fungus, it is said, takes place shortly after germination, the source 

 of infection being the testa of the seed. The infection does not cease with the 

 formation of the mycorrhiza associated with the roots, but affects all parts of 

 the young seedling and most of the mature plant as well. The embryo and 

 endosiDerm of the resting seed seem to be free from infection. It was found 

 possible to sterilize the seed and germinate seedlings free from fungal and 

 bacterial infection, but where the appropriate fungus was not present, seedlings 

 did not develop roots and their growth was checked, although they remained 

 alive for several mouths. The mycorrhizal fungus has been isolated and grown 

 in pure cultures, and sterile seedlings inoculated, thus completing the synthesis 

 of the fungus and the plant. It has not been found possible to replace the 

 stimulus to development which follows seedling infection by supplying various 

 organic nitrogenous substances to the plant. 



A bibliography is given. 



Andropog'on halepensis and A. sorghum, C. V. Piper {Proc. Biol. Soc. 

 Wash., 2S {1915), pp. 25-'i3). — The results are given of a study of many forms 

 of these grasses under cultivation, besides herbarium material in this country, 

 at Kew, and Berlin. These two species of grass are generally treated as dis- 

 tinct species, although there have been published statements indicating that the 

 latter species is derived from the former under cultivation. 



xis a result of his investigations the author considers a more satisfactory 

 treatment of the plants to be to recognize them as two distinct species, A. hale- 

 pensis, perennial plants possessing rootstocks, 5 subspecies or varieties of 

 which are recognized, and A. sorghum, annual plants which become perennial 

 in frostless regions and are without rootstocks. Of the latter species the 

 author enumerates 11 varieties. 



Additional evidence of mutation in CEnothera, II. II. Baktlett {Bot. Gas., 

 59 {1915), No. 2, pp. 81-123, figs. 17). — Studies are reported on mutants of 

 CE. pratincola, a small, recently described self-pollinating species from Ken- 

 tucky, which were brought to maturity and have yielded a second generation. 



The author states that this form is in a condition comparable with that of 

 CE. lamarckiana, the most striking of the mutations (called CE. pratincola num- 

 mularia) occurring in strains from 7 wild mother plants out of 8 selected at 

 random. Two of these strains give mutations in both the Fi and F2 generations 

 from the parent plant and a third strain showed mutations only in the F2 gen- 

 eration. The mutant appears with a fairly uniform frequency of 1 to every 300 



