Mel Hot us alba, L. and other Plants. 67 



qucntly at high altitudes, in strand vegetation, and in tropical 

 and desert areas are special adaptations to prevent a too 

 rapid transpiration. 



In these hot sun positions the plant accomplishes the object 

 of lessening the leaf surface in many different ways. It may 

 be by folding the two halves of the leaves together as in Cro- 

 ton glandulosuvi, by rolling the leaves up as in Rhododendron 

 Cata:obiense, or by folding the leaflets over each other as in 

 Marsilia, or by elevating all the leaflets so that their apices 

 point directly at the sun as in Apios. In this last genus the 

 leaflets become parallel with the sun's rays and thus make 

 little or no shadow. In these different ways the leaves 

 escape much of the heat caused by the sun's rays, and, con- 

 sequently, increased transpiration which would be created 

 thereby. 



Melilotus alba (along with many other genera of Legumi- 

 noscB, such as Robinia, Wistaria, Amorp/ta, PJiascolus, Amphi- 

 carpcza, Gleditschia, Cassia and others), is extremely sensitive 

 to its surroundings, and very readily puts itself, in accordance 

 with external conditions, into any of the three positions men- 

 tioned above. (PI. XIII, Figs. 1, 2 and 3.) 



The day position may always be seen early in the morning. 

 The leaves are spread out in a plane at right angles to the 

 sun's rays. (PI. XIII, Fig 1.) 



The night or sleep position (PI. XIII, Fig. 2, and PI. IX, 

 Fig. 1) is a very interesting one in this plant. From the 

 normal day position the leaflets first sink down so as to make 

 an angle of about forty-five degrees with the surface of the 

 earth below. The terminal leaflet rotates itself on its long 

 axis, either to the right or to the left, through an angle of 

 ninety degrees ; the lateral leaflets now each rotate on their 

 long axis until their edges are toward the zenith. They then 

 approach the terminal leaflet until their upper surfaces nearly 

 or quite touch it. In this position the terminal leaflet has 

 both its faces nearly covered, and the lateral leaflets present 

 their under surfaces only to the external air. A little over 

 one-third of the normal leaf surface is exposed. The torsion 

 takes place in the pulvini of the minor leaf petioles.. This 



