80 KAN'S AS ACADEMY OF SCIENCE. 



or drops to the ground from exhaustion or its own weight. As soon as it has touched 

 something, it makes a short, quick turn and wraps around it, though it may be only 

 another similar vine unable to support it. 



These motions result always in each plant growing in the place that is best 

 adapted to its growth. Why, for instance, does the Ampelopsis virginica climb a 

 tree, or a stone or brick wall in preference to a bush or a haystack ? The tendrils 

 of the Ampelopsis at first, like the tendrils of a grape-vine, seek the dark side of the 

 vine, and finding a solid vertical support that they cannot grasp, accommodate 

 themselves to the conditions and flatten the tips, forming sucking disks that take 

 firm hold of the tree or the face of the brick or stone. Here the vine thrives best; 

 and all that portion of the vine leading to the tree, which may be fifty feet from 

 where the Ampelopsis seed germinated, dies, giving the vine the appearance of hav- 

 ing germinated at the base of the tree or wall. 



A very large wistaria was climbing a stone house, partly by trellis, partly by 

 strings. An apple tree stood near, whose branches reached close to the wistaria 

 vine. Thinking to have part of the wistaria climb the apple tree, I separated some 

 of the vines and laid them over on the branches of the apple tree. But they refused. 

 In three days all the vines had turned toward the house, and some of them had 

 reached back to the main vine by the house. Several attempts of the same kind re- 

 sulted in failure. The vines came back from the apple tree and climbed the other 

 vines by the house at last. The young vines, clinging close to the house, reached 

 far from the supporting trellis, and climbed over the eaves, clinging close by some 

 means, but so effectually that the storms of winter or summer fail to dislodge 

 them. 



A climbing ivy, in order to hold to a tree, sends out numerous rootlets from any 

 place along the dark side of the vine; and the ampelopsis has its sucker-like tendrils 

 at the joints; but how does the wistaria manage to cling ? In this case branches 

 act as tendrils, partly. They bend around projections, and, stiffening with age, 

 hold the vine. Temporarily, leaves do the same thing until the branches have 

 grown. 



Leaves, like flowers, often have certain times of the day for opening and closing. 

 Most noticeable among these are certain species of Euphorbia, notably E. serpylli- 

 folia, E. glyptosperma, E. maculata, E. humistrata, and E. Preslii; also the dogbane 

 Apocynum androsaemifolium. These plants all have opposite leaves, and in the 

 case of the euphorbias, oblique, or lefts and rights; and as soon as the dew begins 

 to fall, they fold together in pairs, as a child folds his hands to pray, and, with the 

 light-colored under-side out, remain thus all night. 



Many of the leguminosse, notably cassia, desmanthus, and desmodium, fold their 

 leaflets at night. These leaflets are jointed to the midrib, and the midrib to the 

 branch, by noticeable articulations that allow a motion of both leaflet and leaf. 

 Daylight opens the leaflets and raises the leaf. Thus, leaves are said to be asleep 

 when they are closed for the night. 



But not all plants fold their leaves with the faces together, as do the plants of 

 the pea family. The sorrel, for example (Oxalis stricta and 0. violacea), folds its 

 leaflets back to back, and the whole leaf droops from its junction with the petiole. 

 Again, Abutilon avicennse, with its very large, velvety leaves, droops straight down 

 from the junction of the blade with the petiole; the petiole remaining in its normal 

 position, and the leaf hanging face outward. 



Everyone, probably, has seen the sunflower turn its leaves eastward to the morn- 

 ing sun, and westward in the evening. Many other plants do precisely the same 

 thing, among which may be noted beans, ragweed, rosinweed, marigold, and many 



