ZOOLOGY AMI BOTANY, MICROSCOPY, ETC. 157 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Structure and Development. 



Vegetative. 



Dorsiventrality in Ficus.* — 0. Triilzsch has studied the causes of 

 dorsiventrality in the stems of Ficus pumila and other similar climbing 

 plants. The author finds that the dorsiventrality of the wood and 

 bast is especially noticeable in that part of the stem nearest to the 

 support, and is the direct result of difference in illumination. There is 

 no transmission of asymmetry to those parts of the stems not within 

 the zone of the unequal illumination. A similar dorsiventrality is 

 found in creeping stems and in steins forced to grow in a bent position. 

 When stems are kept in a bent horizontal position and subjected to a 

 strong unilateral illumination, i.e. when the curvature, the geotropic 

 and the heliotropic factors all act in the same direction, the dorsiven- 

 trality is especially marked. When one or more than one factor acts in 

 opposition to the heliotropic factor, the dorsiventrality represents the 

 resultant of all the factors. The development of the sclerenchyma 

 depends upon the relative dampness of the two surfaces of the 

 climbing stem, the greater moisture of the lower surface preventing any 

 considerable formation. In Ficus pumila, F. scandens, and F. barbata, 

 the aerial roots become dorsiventral when exposed to similar conditions ; 

 tbe same result is also seen in climbing branches of Hedera //el i.e. Gissus 

 antarctica, and Ampelopsis radicantissima, and in the stems of Ricinus 

 communis. The dense formations of aerial roots just below the nodes of 

 Ficus are not to be regarded as the result of those conditions which 

 produce dorsiventrality, but rather as dependent upon dryness and 

 light, both of which inhibit root-formation on the dorsal surface and 

 thus indirectly cause thicker growths on the ventral surface. Moreover 

 rudimentary aerial roots attain full development in the moist, shaded 

 condition of the ventral surface, but are modified into simple organs of 

 attachment on the light, dry, upper surface. The unilateral formation 

 of hairs on aerial roots is also due to relative conditions of light and 

 moisture. The asymmetry of the leaves of Ficus is an inherent 

 character, not dependent on external conditions, while the anisophylly 

 of the stem is a paratonic character brought out under the influence of 

 ■external conditions. 



* Jahrb. wiss. Bot., liv. (1914) pp. 1 -70 (28 figs.). 



