ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 353 



rnoussy state that the first species reaches only a very moderate develop- 

 ment when it does not produce root-tubercles. The second species also 

 is unable to utilise the atmospheric nitrogen without external assistance. 

 It can, however, acquire a normal development without nodosities; but 

 in that case it appears to obtain its nitrogen from bacteria which carry 

 on a parasitic life on certain algae — Phormidium autumnale and Ulothrix 

 Jlaccida — present in the soil. While the root-tubercles of this species 

 sometimes contain bacteria which assist in the nourishment of the host- 

 plant, in other cases the bacteria contained in these nodules appear 

 to exercise no function of the kind, but simply to cany on a parasitic 

 existence on the host. 



Influence of Carbon dioxide on the Growth of Plants.* — M. E. 

 C. Teodoresco has carried on a series of experiments with a number of 

 species of flowering plants, and with Hepaticaa (JSIarchantia polymorphic 

 Lunularia vulgaris), as to the effect on their form and structure of 

 growth in an atmosphere containing more than the normal amount of 

 carbon dioxide (2 per cent.), and growth in an atmosphere deprived 

 as completely as possible of that gas. With the Hepaticae growth is 

 much more luxuriant when the atmosphere contains an excess of C0 2 , 

 and the propagules are formed only in the presence of this gas. With 

 flowering plants, C0 2 appears to retard growth as long as the plant is 

 consuming the food-reserves in the seed ; but after that period, when 

 the amount of C0 2 is increased, the leaves become thicker, the palisade- 

 tissue better developed, and the aeriferous chambers larger both in the 

 palisade and in the lacunar tissue. 



Influence of External Conditions on the Length of the Growing 

 Zone.f — Prof. A. P. Popovicihas carried out a series of experiments on 

 the influence of different conditions of growth on the growing zone, 

 chiefly on Vicia Faba, Phasteolus multiflorus, and Cucurbita Pepo, from 

 which he draws the following general conclusions : — The length of the 

 zone capable of growth varies with the external conditions. This is 

 especially brought out by changes in temperature and in the moisture 

 of the soil. 



Action of Light on the Germination of Seeds4 — In the case of 

 Veronica peregrina, Herr E. Heinricher supplies another example of 

 the influence of light in promoting the germination of seeds. Even 

 a small amount of light makes an appreciable difference, and in full 

 daylight the seeds germinate from five to eight days sooner than in 

 the dark. The rays of the less refrangible half of the spectrum are 

 the most efficient. 



Germination of Cuscuta.§ — By causing a number of Cuscula seeds 

 to germinate in close proximity to one another, Herr W. Kinzel ascer- 

 tained that they put out haustoria which penetrated into others of the 

 seedlings, and that they are, therefore, independent for their develop- 

 ment on the presence of their proper host-plant. 



* Rev. Gen. de Bot. (.Boimier), xi. (1899) pp. 429-44 (11 figs.), 

 t Bot. CentralR, Ixxxi. (1900) pp. 33-40, 87-97. 



1 Ber. Deutsch. Bot. Gesell., xvii. (1899) pp. 308-11. § Tom. cit., pp. 318-9. 

 June 20th, 1900 2 B 



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