186 



true, it may be that the same explanation 

 will cover the case of the red flush so con- 

 spicuous in buds and young- leaves in 

 early spring. It must not be supposed 

 that the need of protection has developed 

 the coloring, but since it is developed it 

 may be of some such service to the plant. 

 Even the conditions which determine au- 

 tumnal coloration have not been made 

 out certainly. 



It is instructive to notice how differ- 

 ently the so-called evergreens, as pines, 

 spruces, etc., have answered the problem 

 of protection against the cold of winter. 

 The evergreens, instead of dropping their 

 leaves, have undertaken to protect them, 

 giving them a small surface and very 

 heavy walls. In this way, protection has 

 been secured at the expense of working 

 power during the season of work. Re- 

 duced surface and thick walls are both 

 obstacles to leaf work. On the other 

 hand, the deciduous trees have devel- 

 oped the working power of their leaves to 

 the greatest extent, giving them large 

 surface exposure and comparatively deli- 

 cate walls. It is out of the question to 

 protect such an amount of surface during 

 the winter, and hence the deciduous hab- 

 it. The evergreens are saved the annual 

 renewal of leaves, but lose in working 

 power; the deciduous trees must renew 

 their leaves annually, but gain greatly in 

 working power. 



To obtain the most striking instances 

 of protection, however, one must exam- 

 ine plants which belong to permanently 

 dry regions, such as may be found in the 

 United States along the Mexican border, 

 or in the regions of tropical deserts. In 

 the first place, it will be noticed that the 

 plants in general produce smaller leaves 

 than in other regions. That this holds a 



direct relation to the dry conditions is 

 evident from the fact that the same plant 

 often produces smaller leaves in dry con- 

 ditions than in moist. One of the most 

 striking features of an arid country is the 

 absence of large leaves. These reduced 

 leaves are of various forms, such as the 

 needle leaves of pines, or the thread-like 

 leaves of certain sedges and grasses, or 

 the narrow leaves with inrolled margins 

 such as is common in many heath plants. 

 The extreme of leaf reduction has been 

 reached by the Cactus plants, whose 

 leaves, so far as foliage is concerned, have 

 disappeared entirely, and the leaf work is 

 done by the surface of the globular, cylin- 

 drical, or flattened stems. A covering of 

 hairs is an effective sun screen, and it is 

 very common to find plants of dry re- 

 gions characteristically hairy. In such 

 regions it is to be observed also that 

 dwarf growths prevail, so that the plant, 

 as a whole, does not present such an ex- 

 posure to the drouth as in regions of 

 greater moisture. One of the most prom- 

 inent measures of protection in dry re- 

 gions is the organization of what are 

 known as water reservoirs. Nearly all 

 plants of such regions have leaves which 

 are known as fleshy, that is, they are 

 thick and juicy, being reservoirs of stored 

 up moisture which is doled out cautiously 

 according to the needs of the plant, with- 

 out any wastefulness. 



The whole subject of plant protection 

 is an immense one, and the illustrations 

 given above are merely intended to sug- 

 gest that there is such a subject, and to 

 lead to some observation of the various 

 schemes of protection which are to be 

 seen plainly on everv hand. 



John Merle Coulter. 



Nature is but a name for an effect 

 Whose cause is God. 



— Cowper, "The Task." 



