ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 373 



to determine tliis question experimentally, by immersing pollen-grains 

 in a mixture of gelatine (first warmed) and a solution of sugar, with a 

 very small quantity of extract of meat, iu which nutrient fluid they 

 readily put out their tubes. He finds that neither the spot to which 

 the pollen-tube attaches itself, nor the direction which it afterwards 

 takes, nor the rapidity of its growth, is in any way aifected either by 

 gravitation or by light, or by contact with a solid substance. Similar 

 experiments on four fungi, Miicor Mucedo, M. stolonifer, Trichotliecium 

 roseum, and Eurotium repens, yielded similar results as far as gravi- 

 tation was concerned, this force appearing to exercise no influence on 

 the direction or rapidity of growth of the mycelial filaments, nor on 

 their branching. 



Water Distribution in Plants.* — G. Kraus having expressed 

 and filtered the sap of Lonicera tartarica and Datura, and taken 

 the specific gravity with the usual precautions, found it varied 

 between 1*03 and 1'0059. The juice of sugar-beets ranged 

 between 1*057 and 1'074. The specific gravity of the sap in the 

 growing twig was found to be less in the older than in the younger 

 portions, and growth was invariably accompanied by dilution of the 

 sap, owing to constantly increasing absorption of water. The free 

 acids and albumen also decreased in percentage, but increased in 

 actual quantity. The increase in sugar during growth was remarkable ; 

 it increased with great rapidity up to a certain point, when it again 

 declined, so that there is a maximum point in sugar contents, which 

 is not at all coincident with the maximum of growth. 



An extended series of observations shows that in crooked plants 

 the under or convex side contains sap of less concentration, and 

 poorer in free acid and sugar, not only relatively, but absolutely. 

 Horizontal branches are richer in sugar than vertical. When plants 

 are shaken so as to bend their tops towards the ground, an immediate 

 increase of specific gravity in the sap, and an increase of sugar in the 

 under or convex part of the bend takes place, showing that the sugar 

 is in actual process of formation at the time of bending. 



Causes of the Movement of Water in Plants.f — J. Boehm 

 adduces experimental evidence in favour of his theory, already pub- 

 lished, that the main factor in causing the motion of water in plants 

 is not osmose, but the unequal pressure in different cells caused by 

 the constant variation in the intensity of transpiration. 



" Compass-flowers." | — E. Stahl gives the results of his experi- 

 ments with Lactuca Scariola and SilpMum laciniatum for the purpose 

 of ascertaining the conditions which cause their leaves to assume a 

 meridional position. In the case of SilpMum, the common " Compass- 

 plant" of the Western States of America, the fact that the leaves 

 point in a north and south direction has long been known, but in 



* Bied. Centr., 1881, pp. 630-2. Journ. Chem. Soc, xlii. (Abstrac(s), 1882, 

 p. 327. See alao this Journal, iii. (1880) pp. 294-5. 



t Bot. Ztg., xxxix. (1881) pp. 801-13, 817-27. 



t Jen. Zeitschr. f. Naturw., xv. (1881) pp. 381-9 (1 (pi.). Cf. Amer. Journ, 

 Sci., iii, (1882) pp. 159-60. 



