ZOOLOGY AND BOTANY^ MICROSCOPY, ETC. 413 



movements is very small, viz. from O'Ol to 0*1 per cent., in com- 

 bination with any base (sodium malate was most commonly used); it 

 is perceptible even wben tlie proportion is so small as O'OOl per 

 cent. Free malic acid has the same effect as an alkaline salt in very 

 dilute solutions ; but when more concentrated it has precisely the 

 opposite effect, causing repulsion. A repulsion is effected by a mix- 

 ture of 0*01 per cent, malic acid and 0*2 per cent, citric acid; or 

 by 5 per cent, neutral sodium malate. 



The presence of so small a quantity as • 001 per cent, of cane sugar 

 has a corresponding attractive force on the antherozoids of mosses. 

 The specific attracting medium has not yet been ascertained which 

 causes the collection of antherozoids around oospheres, as in the 

 case of Fucus. 



Bacterium Termo and Spirillum undula were powerfully attracted 

 by a 1 per cent, solution of extract of meat or of asparagin ; a higher 

 degree of concentration repels the latter. 



The author suggests that the familiar bending of organs in the 

 case of carnivorous plants is due to similar causes. 



Direct Observation of the Movement of Water in Plants.* — 

 G. Capus gives the following account of experiments on this subject, 

 chiefly on the dahlia. 



By means of a flat razor a tangential section is made in an inter- 

 node, a few centimetres in length, cutting into the stem nearly to the 

 depth of the vascular bundles ; this cut must be slightly concave. 

 On the opposite side of the stem, and at the same height, two notches 

 are made penetrating to the pith, allowing this part of the stem to be 

 raised so as to expose the medullary canal or pith. This is carefully 

 taken out without cutting the primary wood at the bottom ; a trans- 

 parent section is thus obtained in which the vessels may be examined 

 intact. 



The Microscope is placed horizontally in front of the section 

 prepared in this way on a cathetometer. The plant may be observed 

 either growing in the open soil or in a pot. On the section is placed 

 a drop of water flattened by a cover-glass fixed to the stem by a drop 

 of Canada balsam, or held simply by capillarity. The section is then 

 placed opposite the light, when the vessels and fibres of the wood 

 are seen to be full of bubbles of air more or less numerous in strings. 

 When the weather is damp, the sky cloudy, and the ground saturated, 

 the plant contains more water, and there are but few bubbles of air. 

 They are in greater numbers and larger when the weather is dry, and 

 the plant directly exposed to the sun. As soon as the sun no longer 

 shines on the plant, the bubbles of air diminish in size in the vessels 

 and finally disappear, absorption from the roots exceeding transpi- 

 ration. When, on the contrary, transpiration is relatively active, the 

 index indicates the ascending movement of water in the vessels. 



Kheotropism.l — This term is applied by B. Jonsson to the in- 

 fluence of running water on the direction of growing plants and parts 



* Comptes Eendus, xcvii. (1883) pp. 1087-89. 

 t Ber. Deutsch. Bot. Gesell., i. (1883) pp. 512-21. 



