AGRICULTURAL BOTANY. 933 



restored to the lislit. luvestiKations with l'<in</iuiii cdtilc showed that light 

 had no part in the formation of hydrocyanic acid, except as it favored photo- 

 synthesis. Stndies with Phascolns luantus confirmed this conclusion and 

 showed that carbohydrates and especially dextrose are essential to cyano- 

 geuesis, light playing no part in it except as it is necessary for the formation 

 of carbohydrates. The cells that noi-mally produce hydrocyanic acid are 

 formed in darkness, provided the supply of carbohydrates is sufficient. An 

 abnormal fluctuation in the hydrocyanic acid content of leaves of P. lunatus 

 and a number of other plants was ncited. the maximum occurring about noon. 



On the protective influence assigned to hydrocyanic acid in plants, M. 

 Treub (Ann. Jard. Bot. Buitcnzorg, 2. set:, 6 (1907), pt. 1, pp. 107-114, pis. 2).— 

 As the result of the examination of a number of species of plants, the author 

 denies that the hydrocyanic acid in the plant has in general a protective 

 effect. While some enemies may be warded off by its presence, others seem to 

 be attracted, and the toxicity of the hydrocyanic acid plays no role in the 

 economy of the plant. 



The role of potash in the plant organism, P. Vageler (Umschau, 12 {1908), 

 No. 1, pp. 5-7, pi. 1). — The author reviews some of the literature relating to 

 the role of potash in the plant organism, pointing out its effect on the assimi- 

 lative processes, carbohydrate formation, etc. Attention is also called to the 

 undoubted effect a deficiency of potash exerts on the susceptibility of plants 

 to disease. 



On nutrient and balanced solutions, W. J. V. Osteehout ( JJniv. Cal. Pubs., 

 Hot.. 2 {1907), No. 15, pp. 317, 318). — The author discusses the difference be- 

 tween nutrient and balanced solutions, the difference depending, according 

 to him, on the fact that salts have two distinct functions, namely, nutritive 

 and protective. The protective function is exercised when a poisonous salt 

 has its toxic effect counteracted by the addition of another salt, thus producing 

 a balanced solution. The author notes the balancing eft'ect of strontium, barium, 

 and calcium on the poisonous properties of magnesium, sodium, and potassium. 

 It is stated that a nutrient solution may serve its purpose very well so long 

 as used in a very dilute form, but if the concentration is increased there is 

 soon reached a point where toxic effects intervene, and these must be counter- 

 acted by the addition of suitable protective salts. When this is done a bal- 

 anced solution is obtained. 



The author shows that while, according to the researches of Pasteur, Raulin, 

 tind others, calcium is not needed for the nutrition of fungi, yet when the 

 concentration of the solution is increased so that it becomes toxic, the addition 

 of calcium has a protective value for fungi just as for other plants. 



Culture of micro-organisms, E. Kijster {Kultur der Mikroorganismen. 

 Leipsic and Berlin, 1907, pp. 11+201, figs. 16). — This book is presented as 

 a guide to the culture of micro-organisms and is intended for use in zoological, 

 botanical, medical, and agricultural laboratories. After describing in general 

 the methods to be pursued, the author takes up a discussion of nutrient media 

 and their preparation and the making of cultures, after which special direc- 

 tions are given for the cultivation of protozoa, flagellata, myxomycetes, algse, 

 fungi, and bacteria. 



On the importance of pure cultures, O. Richteb (Die Bedeutung der Rein- 

 kultur. Berlin, 1907, pp. VI II + 128, figs. 3). — In this work, which is a liter- 

 ature study, the author jioints out the necessity for pure cultui'es of micro- 

 organisms in carrying on physiological and other studies. 



