ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 67 



case reach the level of the soil. They branched much less freely than 

 normal soil roots. 



Distribution of Essential Oil in an Annual Plant.* — E. Charabot 

 and G. Laloue find that a gain in the amount of essential oil in the 

 inflorescence is balanced by a loss in the green organs, and vice versa. 

 Their results suggest that the essence is first carried from the leaves to 

 the flower, acting as a carrier for the carbohydrates which are to nourish 

 that organ. After fertilisation, when the storage of carbohydrates is 

 completed and the influx of nutriment into the flower ceases, the 

 essential oil seems to return to the green organs. As regards distribu- 

 tion among the different plant-members, the authors find that the root 

 contains no essential oil, the stem only a small amount, while the leaf 

 and inflorescence are the richest. 



Sense-organs of Plants.! — G. Haberlandt describes the various types, 

 of structure, bristles, hairs and papilla? which serve for the perception 

 of mechanical stimulus, and also gives an account of the statolith 

 theory, in which both he and Nemec found an explanation of the sensi- 

 tiveness of plants to the force of gravity. He also discusses his recent 

 theory of the mechanism by which plants perceive the direction of 

 incident light. The epidermal cells act as the sense-organs. When 

 light strikes a leaf at right angles to the surface, it results from the 

 plano-convex form of the epidermal cells, that the inner wall of each 

 cell is illuminated more brightly in the centre than at the periphery. 

 If the light strikes the leaf obliquely, the bright patches on the inner 

 cell walls are no longer central. This change, it is suggested, con- 

 stitutes a stimulus calling forth a curvature of the leaf-stalk by which 

 the leaf is brought again to its normal position at right angles to the 

 incident light ; the leaf moves when the bright patch is not central, 

 and comes to rest when each of its epidermal cells is centrally illu- 

 minated. 



Appreciation of Depth in Rhizomatous Plants. :j: — C. Raunklaer 

 finds as the result of experiments with Polygonatum multiflorum, that 

 when placed at a certain level in the soil the rhizome is transversely 

 geotropic, while at every other depth its geotropism changes, so that it 

 becomes more and more positively geotropic as we approach the surface, 

 and more negatively geotropic at increasingly lower levels. Thus the 

 rhizome responds to changes in the direction of its growth, so as to 

 maintain itself at a definite depth which is favourable to its develop- 

 ment. That whicli indicates to the plant the depth at which the 

 rhizome is buried is the distance which separates it from the level at 

 which the aerial shoot reaches the light. 



Formation of Roots and Shoots in Cutting's. § — E. Kiister de- 

 scribes experiments which suggest that the polarity shown in cuttings 



* Comptcs Eendus, cxxxix. (1904) pp. 92S -9. 



+ Die Sinnesorgane der Pflanzen. By G. Haberlandt. 46 pp., Earth, Leipzig, 

 1904. See also Nature, lxxi. (1904) pp. 123-4. 



t Oversiirt. k. Dansk. Vidensk. Selsk. Forhandl,. 1904, pp. 329-49 (5 figs, in text). 



§ Ber. Deutsch. Bot. Gesell.,xxii. (1904) pp. 167-70(1 pi. 1 ); Jahrb. wiss. Bot, xL 

 (1904) pp. 279-302 (4 rigs.). See also Bot. Gazette, xxxviii. (1904) p. 390. 



