10 



equally shaded in a dark thicket and never exposed to direct 

 sunlight, show no upward turn. In the first instance, the plant 

 had been accustomed to daily exposure to sunlight at midday, 

 and hence the motion in its leaves is probably due to the after 

 effect. No such after effect would be possible, of course, in a 

 plant continually shaded. 



While the position of the leaflets in direct sunlight is an 

 edgevrise one, and while such a position in the case of the lateral 

 leatiets might be reached by a mere twist of ninety degrees, 

 Erythrina prefers to bend the pulvini in attaining it. In all 

 eases there is an attempt on the part of the plant to bring the 

 tip of each leaflet toward the sun rather than the side edge. 

 For instance, if a leaf lies horizontally, its leaflets expanded, 

 -with their spongy parenchyma sides downwards, the pulvini 

 l)y twisting would bring their blades edgewise. Ethyrina, how- 

 ever, bends its pulvini ninety degrees upwards, thus bringing 

 the tips of the leaflets towards the sun. If a leaf lies with 

 its midrib pointing directly upwards, its terminal leaflet towards 

 the sun, the expanded position of the leaf would mean an edge- 

 wise position for all its leaflets. Thus they would all be pro- 

 tected from intense sunlight. Yet the tips of the lateral leaflets 

 point outwards, not upwards, and so a bend in their pulvini 

 occurs which results in their tips being directed towards the 

 sun. Such position has in it no greater merit as a protective 

 feature than the expanded one, unless it be the huddling of 

 the leaflets and a consequent slight reduction of transpiration in 

 the terminal leaflet. 



In the extreme direct sunlight position of the leaflets in 

 Erythrina, the under or stomata-bearing surface is outwards or 

 exposed to diffuse light and to wind. As was mentioned near 

 the beginning of the paper, such an arrangement is scarcely 

 conducive to lessening transpiration. If this is the desideratum, 

 then a method having a semblance of efficiency, would be a 

 vertical position with tips downwards so that the stomata-bearing 

 surfaces might be together. As this does not occur in Ethyrina, 

 it is reasonable to suppose that so far as this species is concerned, 

 too great light intensity is feared rather than too rapid trans- 

 piration. 



An a prhiri conclusion as to the rapidity of assumption of the 

 expanded condition following closure due to direct sunlight, is 



