456 SUMMARY OF CURRENT RESEARCHES RELATING TO 



that though they do not directly collect nitrogen, yet, indirectly, they 

 are of immense importance, as they furnish carbon material in the form 

 of mannite, glycogen, etc., to the nitro-bacteria. The fungi experimented 

 with were Phoma Beta, Aspergillus niger, Penicillium glaucum, and 

 Mucor stolonifer. 



Irritability. 



Effect of Light on Green Plants in absence of Carbon-dioxide.* — 

 Jules Lefevre has experimented with Lepidium sativum grown in arti- 

 ficial soil containing amido-compounds, and watered with water free 

 from C0 2 . One set of plants was placed under a bell-jar, in presence 

 of baryta, and in full sunlight, while a second set was under similar 

 conditions, but in darkness. The dry weight of the first set was greatly 

 increased compared with the previous dry weight when grown in air 

 under similar conditions ; the second set died in a week, and its weight 

 was slightly less. 



The author concludes that the synthesis performed by green plants 

 in absence of C0 2 , and in an amido-soil, becomes impossible in the 

 absence of light ; also, this synthesis is essentially a chlorophyll function. 



Modifications of Tropical Plants in changed Surroundings.! — 

 D. Bois and J. Gallaud have investigated the reason for deterioration in 

 the commercial products of such plants as Ginnamomum Gamphora, Ficus 

 elastica, etc., when removed from their native habitat to surroundings 

 which appear to be favourable to their cultivation. Their experiments 

 were carried out upon various species of Euphorbia, and they conclude 

 that there is no ground for attributing the change to accidental, in- 

 dividual variations. They find that in both the secretory and support- 

 ing tissues (which are the chief sources of the commercial products), 

 marked and rapid changes occur, directly resulting from differences in 

 external conditions, such as heat, humidity, etc. More attention must 

 be paid to these points, if better success is to attend the acclimatising of 

 such plants. 



Action of Sulphur-dioxide on Plants.! — A. "Wieler finds that 

 different plants and organs are unequally sensitive to sulphur-dioxide, 

 but that all plants within 8 kilometres from the source of pollution have 

 the dioxide in their leaves. It enters through the stomata, and exerts 

 an adverse influence on photosynthesis, owing to its direct action on the 

 chloroplasts. Transpiration is unaffected. Injured plants decrease in 

 height, and have premature autumnal coloration and leaf-fall. The 

 author considers that the dioxide unites with metabolites, especially 

 aldehydes, with liberation of sulphuric acid, and to the latter the injury 

 is due. Indirectly the dioxide affects the soil by removal of its basic 

 constituents, thus causing an accumulation of humic acids. Plants ex- 

 posed to the action of a high percentage of the dioxide for a short 

 time are acutely affected and past remedy. Those under the action of a 

 low percentage for a long time exhibit the same characters as when 



* Comptes Rendus, cxli. (1905) pp. 1035-6. 

 + Tom. cit., pp. 1033-35. 



J Berlin : Borntraeger, 1905, vii. and 427 pp. See also Nature, lxxiii. (1906) 

 pp. 385-6. 



