185 



nary protective coats. In the spring the 

 seed leaves of numerous seedHngs may 

 be seen at the approach of night to rise 

 upward and come together, just as the 

 pahiis of the hand may be placed together 

 over one's head. This reduces the sur- 

 face of exposure and the danger of chill 

 at least one-h^f. Darwin experimented 

 upon these seedlings, and discovered that 

 by preventing some of the seed leaves 

 from moving, the seedlings were serious- 

 ly injured. The leaves of very many 

 plants assume a peculiar night position 

 which tends to meet the danger of loss of 

 heat. Often the three leaflets of the com- 

 mon clover, if growing in an exposed 

 place, may be observed to fold together 

 into a sort of tent-like arrangement. 



Many plants are also observed to pro- 

 tect themselves against rain, as it is nec- 

 essary for leaves to avoid becoming wet. 

 If the water is allowed to soak in, the 

 work of the leaves is at once interfered 

 with. Hence it will be noticed that most 

 leaves are able to shed water, partly by 

 their position, partly by their structure. 

 In many plants the leaves are so arranged 

 that the water runs off toward the stem ; 

 in other plants the rain is shed outwards 

 as from the eaves of a house. Some of the 

 structures which prevent the rain from 

 soaking in are a smooth epidermis, lay- 

 ers of cuticle, hairy coverings, etc. In- 

 teresting experiments may be performed 

 with different leaves to test their power 

 of shedding water. If a gentle spray be 

 allowed to play upon different plants it 

 will be observed that the water glances 

 off at once from the surfaces of some 

 leaves, runs off more slightly from oth- 

 ers, and may be more or less retained by 

 others. 



Perhaps the most general preparation 

 for protection in our region is that which 

 is made for the coming of the winter's 

 cold. In many cases plants do not at- 

 tempt to protect their delicate structures 

 from the severity of winter, but disap- 

 pear entirely, leaving only well-protected 

 seeds to carry them over into the next 

 growing season. This results in the so- 

 called "annual habit," which has been 

 learned by many plants in order to es- 

 cape a season of danger. Other plants 

 do not disappear so completely, but ev- 



erything above the surface of the ground 

 dies, while the plant continues in the 

 form of underground bulbs, tubers, or 

 various thickened structures. This hab- 

 it of seeking a subterranean retreat at 

 the approach of some dangerous sea- 

 son is a very good one, and is found in 

 many of our early spring plants. This 

 subterranean habit has a great advantage 

 over the annual habit, since a seed is very 

 slow in bringing the plant back again, 

 while a bulb can produce its plant very 

 rapidly. 



Still other plants preserve more of 

 their structures than either the annuals 

 or the ground-loving plants. For exam- 

 ple, most of our trees have cultivated 

 what is known as the deciduous habit, 

 that is, they merely drop their leaves, 

 which are the endangered structures, at 

 the approach of the unfavorable season, 

 and renew them again when the favorable 

 conditions return. It should be remark- 

 ed that these leaves do not fall because 

 they are broken off, but that in a certain 

 sense it is a process of growing off, which 

 is carefully prepared for. One of the 

 most prominent features associated with 

 the deciduous habit is the autumnal col- 

 oration. The vivid colors which appear 

 in the leaves of many trees just before the 

 time of falling have attracted a great deal 

 of attention, but although it is so promi- 

 nent, the causes for it are very obscure. 

 It will be noticed that this autumnal col- 

 oration consists in the development of 

 various shades of two typical colors, yel- 

 low and red. It is known that the yellow 

 is due to the breaking down of the green 

 substances, so that it simply indicates a 

 post mortem change, as may be noticed 

 in connection with the blanching of cel- 

 ery in which the leaves and upper part of 

 the stem may be green, the green may 

 shade gradually into yellow, and finally 

 into the pure white of complete blanch- 

 ing. The red coloring matter, however, 

 is very different. Certain experiments 

 upon plant colors have indicated that the 

 presence of the red slightly increases the 

 temperature by absorbing more heat. It 

 is suggested that the red color may be a 

 slight protection to the living substance 

 which is ceasing to work, and which is in 

 danger of exposure to cold. If this be 



