1899] SALT-DEVELOPED SUCCULENCE 187 



absorption by the plant a matter of considerable difficulty, that in 

 short the conditions of life might be described in the well-known 

 words " water, water, everywhere, but not a drop to drink." 



Schimper's experiments (" Indo-malayische Strandflora ") suggested 

 that salt exercises a poisonous influence on plant life, and he concluded 

 that structural adaptations directed towards the reduction of transpira- 

 tion were brought about by the necessity of keeping the relative amount 

 of salt in the cell sap below a certain point, which varies with the 

 species. 



Stahl {Bot. Zcit. 1894) pointed out from observations on artificial 

 cultures that the stomata of Halophytes are completely paralysed, the 

 apertures remaining permanently open, thus compelling the plant to 

 take refuge in other structural modifications in order to limit the 

 transpiration current ; hence the succulence. 



Professor Diels (Pringsheim's Jahrb. f. Wiss. Bot. xxxii. 1898) 

 lias been unable to discover in plants growing under natural conditions 

 any stomatic paralysis such as that described by Stahl, and he also 

 differs from Schimper in holding that the concentration of sodium 

 chloride is kept below the danger point, not by limitation of transpira- 

 tion, but by a chemical decomposition of the salt which at the specific 

 limit of concentration balances the absorption. The process of respira- 

 tion in succulents differs from that in other plants in that oxidation 

 does not proceed quite so far, but stops at malic acid or some isomer 

 with which the cell sap becomes saturated, while only small quantities 

 of carbonic acid are evolved. 



Professor Diels employs this inherent acidity of temper, only 

 obtainable by the development of succulence, in decomposing the 

 excess of sodium chloride, with the result that the plant is enabled to 

 exist unharmed in the bitter waters of its Marah. The chemical 

 process by which the decomposition of the salt is effected is not as yet 

 known, but the author assumes that the malic acid combines with the 

 sodium to form a salt which is of further use in the plant economy, 

 while the hydrochloric acid is excreted by the roots. 



Chalazogams 



Since Treub first called attention to the chalazogamy of Casuarines 

 (Ann. Jard. Bot. Buitcnzorg, 1891) many examples of the non- 

 micropylar growth of the pollen tube have been recorded, and the 

 theory of the evolution of normal porogamic dicotyledons from the 

 chalazogamic type has been steadily upheld by several botanists, 

 among whom perhaps the best known is Professor Nawaschin. 



In his most recent paper (" Ueber das Verhalten des Pollen- 

 schlauches bei der Ulme," Bull. Acad. Sci. St. Pctcrsbourg, 1898) 



