190 SUMMARY OF CURRENT RESEARCHES RELATING TO 



plants is about 1 to 2 p.c. Growth of the root began to be checked 

 with 5 p.c. C0 2 , and was stopped with 25 to 30 p.c, in the case of the 

 stem the percentages were 15 and 20 to 25 respectively. In the case of 

 seedlings of barley, an exposure for 24 to 48 hours to 25 to 40 p.c. of 

 the gas exercised no recognisable injurious effect on the root, while the 

 stem was able similarly to resist an exposure for the same period to a 

 20 p.c. atmosphere. 



Spore-germination was inhibited by 60 p.c. C0 2 in the case of Mucor, 

 100 p.c. in the case of Aspergillus and of Penicillium, while growth of 

 Mucor was checked in an atmosphere containing 30-40, and the other 

 two moulds in one containing 80 p.c. of the gas. Ripe spores were 

 formed as long as the t amount of C0 2 did not exceed 10 p.c. in the 

 case of Mucor, 50 p.c. in the case of Penicillium, and 40 p.c. with 

 Aspergillus. 



Nitrogen Assimilation in Moulds.* — F. Czapek has studied the 

 utilisation of amines, amides, and ammonium salts in the production of 

 proteids in Aspergillus niger. Suitable sources of nitrogen were found 

 among primary, secondary, and tertiary amines, whilst quaternary am- 

 monium compounds are very injurious. The suitability of alkylamines 

 as a source of nitrogen increases with the amount of carbon and the 

 molecular weight. Isomeric compounds show marked differences ; the 

 presence of hydroxyl groups is favourable. Acetamide and propion- 

 amide are good sources of nitrogen, whilst the other amides of the 

 series are unsuitable. Amides of dibasic acids gave good results. 

 Nitrites are on the whole unsuitable. Amidines are good sources. Urea 

 and its derivatives are inferior to amino-acids and alkylamines. Am- 

 monium salts of the acetic acid series are not on the whole suitable as 

 sources of nitrogen, whilst the salts of the oxalic acid series proved to 

 be very suitable. Good results ensued with ammonium oxalate when 

 carbon was supplied in the form of sugar. 



^Effect of Composition of Soil on Plants.f — H. B. Dorner studied 

 the effect of difference of soil, namely loam, clay, and sand on a few 

 common plants,— carnation, chrysanthemum, geranium, bean, corn, and 

 onion. The differences are more marked in the gross than in the minute 

 structure, being general in the former for all -the plants studied, while 

 changes in minute structure are more specific in nature. The effect of 

 a heavy clay upon a plant is almost the same as that of sand. This 

 may be partly explained by the fact that although a clay soil is very 

 rich in plant foods, the roots find such difficulty in penetrating it that 

 the greater part is unavailable. A change in soil from loam to sand 

 was found to produce a decrease in general size, and also in leaf -surface, 

 length of petioles, diameter of stem, and length of internodes, also 

 a decrease in the mass of roots, except in the onion ; if, however, the 

 size of the plants be considered, the mass of roots of plants in the sand 

 was always relatively the greatest. Thus the plants in the sand have a 

 stunted growth above soil and an increased growth in the soil. This 

 is also true of the clay, but to a less extent than of the sand. The clay 



* Beitr. Chem. Physiol. Path., 1902, ii. pp. 557-90. See also Journ. Chem. Soc, 

 lxxxiv. (1903) ii. p. 35. 



t Proc. Indiana Acad. Sci., 1901 (1902) pp. 284-90 (2 pis.). 



