'^ ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 669 



dovsiventrality be reversed. In certain plants the oiientation of tlio 

 dorsiventral structure of lateral branches can be determined by external 

 agencies ("ex. Columnea Schiedeana, Scntdhma alhida). Often, how- 

 ever, it is independent of external agencies, and is dcterminel solely by 

 the motlier-axis. In certain phxnts the lateral branches are dorsi- 

 ventral, the primary axis remaining radial fex. CaUisia delicatula, 

 Cyanotis cristata) ; more often, however, the primary axis itself bt comes 

 dorsiventral sooner or later. In all the ])lants studied in which the 

 primary axis became dorsiventral, except Cicer arietinuni, the dorsi- 

 ventral structure of this axis could be determined by light or gravita- 

 tion. When the dorsiventral structure is determined by light, the 

 illuminated suiface usually becomes superior, and in normal conditions 

 faces upwards. 



One-sided Hardness of Wood.* — According to Herr P. Kononczuk, it 

 is especially common in conifers for the annual rings to be very much 

 thicker on one side of the branch or stem than on the other side ; and 

 the wood is then harder on that side where the rings are broadest. In 

 the case of horizontal or oblique stems or branches, this is always the 

 case on the under side, and is due to gravitation ; in the case of erect 

 stems, it is found on that side which jn'oduces the greatest number of 

 branches, i. e. that one most exposed to the air, or especially on the east 

 or south side. 



Influence of Exposure on the Growth of the Park of Conifers, t— 

 From the result of a large number of observations, M. E. Mer finds that 

 in pine-trees the sides most exposed to the heat of the sun, i. e. tlie south 

 and west, have a thicker bark relatively to the thickness of the wood 

 than those not so fully exposed. Exposure to heat and light retard the 

 formation of wood relatively to that of the bark. 



Chlorophyllous Assimilation and Transpiration.^ — M. H. Jumelle 

 describes certain experiments made with the object of ascertaining whether 

 there exists any relation b:^tween the two phenomena of chlorojjhyllous 

 assimilation and transpiration ; in other words, whether, if one of them 

 is arrested the other is modified. The conclusions of the author are 

 that the jn-esence of carbon dioxide in the air, or the presence of potash, 

 which might ace :lerate the transpiration by drying the air, has really 

 no sensible effect on transpiration ; but that if the function of the 

 chlorophyll persists while assimilation is suspended, the intensity of 

 the transpiration is auginent'jd. This accords with the theory of 

 Weisner, who maintains that a portion only of the light which traverses 

 the chlorophyll takes part in the decomposition of the carbon dioxide, 

 the heat provided by the other portion producing the transpiration ; 

 that is, if assimilation is suj)j)iessed, that portion of the luminous ray 

 which serves for the decomposition of the carbon dioxide remains free. 

 The result is that more heat is developed, and consequently a larger 

 amount of transpiration takes jjlace. 



Influence of Mineral Substances on the Growth of Plants.§ — By 

 contrasting the development of plants (chiefly lupins) grown in distilled 



* Jahrb. St. Petersb. Forstiiistit., ii. (ISS8) pp. 41-56 (4 pis.). See Bot. 

 Oentralbl., xxxviii. (188'.)) p. 794. 



t Journ. de Bot. (INIorot), iii. (1889) pp. 52-9, 77-83, 106-12, 114-21, 136-40. 

 Of. this Journal, 1888, p. 762. 



J Rev. Gen. de Bot. (Bonnier), i. (1889) pp. 37-46. 



§ Couiptts Rcndus, cviii. (1889) pp 466-8. 



