CHAPTER XV 



the mountain flora in the north, but in the San Bernardino moun- 

 tains there are literally acres of Pentstemon and Castilleia at altitudes 

 of seven or eight thousand feet, and scattered scarlet flowers every- 

 where. For two months in the mountains, I daily watched humming 

 birds visiting flowers from dawn to twilight, and I never once saw 

 them visit any but scarlet flowers. In the valleys, they frequently 

 avail themselves of the hospitality of flowers of other colors, but 

 where there is a great abundance of flowers of all colors, their behav- 

 ior leaves one in little doubt as to their color preference. 



The methods of climbing plants are full of interest, and form the 

 subject of considerable botanical literature ; they can be easily studied 

 in the home garden during the summer vacation. Four different 

 types have already been noted among native plants ; the Pentstemon 

 cordifolius, the blackberry and the Nemophila aurita, climb by weav- 

 ing or looping themselves over underbrush ; the morning-glory and 

 dodder climb by means of their twining stems, the chilicothe and 

 grape, by tendrils, and the poison oak by rootlets. Encourage the 

 children to find further illustrations of these types among cultivated 

 plants. The climbing roses weave their way up on lattices, just as 

 the Nemophila or the blackberry clambers over bushes, the prickles 

 always assisting in the process. The best way to study twining plants 

 is to watch morning-glory seedlings when the upper portion of the 

 young shoot begins its sweeping motion, before it has found a support. 

 In this way it will be seen that there actually is motion, not merely 

 growth, around the support. This motion is called circum nutation ; 

 it is not twisting, but the stem bends successively to all points of the 

 compass. The books explain that circumnutation is due to a line of 

 turgescence, that is, of much distended cells, which by moving about 

 the stem, causes it to bend always in the opposite direction ; but what 

 impels the protoplasm that controls the turgescence cannot be 

 explained. A very vigorous morning-glory stem upon a warm day 

 completes a revolution in two or three hours, so the motion may be 

 easily perceived. Twining plants need slender supports, and in tem- 

 perate climates it is usually only annuals that choose this method of 

 getting up in the world quickly. When a perennial twines about a 

 perennial stem either one or the other must be ultimately destroyed, 

 since as the supporting stem increases in circumference, either it must 

 be strangled, or the twining stem ruptured. Let children observe 

 whether the direction of the twining is clockwise or the reverse. I 

 know but one plant, the so-called smilax, that twines sometimes in 

 one, sometimes in the other way. The best device of all for climbing 

 is by means of tendrils, and here again there is much diversity of 



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