DRY FARMING CONGRESS. 



243 



power of some of the winds which sweep over the prairie and desert re- 

 gions. Even in the Kaw Valley of central Kansas I have seen a March 

 wind so drying in its nature that young leaves upon lilac, elm and mul- 

 berry trees just showing the fr6sh tender green which indicated the ad- 

 vent of spring were rolled up, dried and strewn upon the ground in 

 handfuls, for all the world like dried tea leaves. Centuries of adaptation 

 to climatic conditions where such winds are liable to prevail cannot but 

 develop, generation after generation, individuals having characteristics 

 which enable them to resist to the greatest degree possible these drying 

 influences. There are two m.ain types along which these developments 

 take place — in one case, many leaves are retained upon the plants but 

 these either possessed of a pubescent, or a resinous or varnished coating, 

 or of a tough, leathery structure and a peculiarly arranged system of 

 cells, which enables them to resist to the utmost the transpiration of 

 the precious particles of water. 



In the other type of plants, the leaf system becomes almost want- 

 ing. The leaves are few, greatly reduced in size, even to mere scales 

 barely indicating the position at which normal leaves would have occurred, 

 and the work of assimilation is performed by means of a greatly developed 

 addition to the chylorophyll cells in the stems themselves. Of course, 

 familiar examples of these types are met with in the cacti and more es- 

 pecially the prickly pears. Examples much less familiar are found in 

 many trees and shrubs of the order Leguminosae, notably species of the 

 Palo Verde and still more strikingly in the genus Dalea. In the Palo 

 Verde we have a much-branched tree, whose entire trunk, branches and 

 twigs are of a vivid green color. It is armed, as most desert plants must 

 be, with innumerable spines, which represent the suppression of tiny twigs 

 and branches. The compound leaves are very slender, the leaflets re- 

 duced to less than a quarter of an inch in length, oftentimes so small as 

 to require close inspection to detect them. In the Dalea, notably Dalea 

 spinosa, we have a much-branched, low tree of a dull lead or smoke color, 

 armed w^ith a remarkable system of spines or thorns, and with its leaf 

 system so reduced as to be very difficult to detect at all. Yet each of 

 these trees is capable of. producing in a very short time a dense covering 

 of blossoms, making them objects of beauty well worth a l(3ng journey to 

 see. Pods are set and seeds developed in a remarakbly short time, and 

 apparently the remainder of the summer sperit in simple resistance to the 

 fierce heat of the region. 



The familiar milkweed, or Asclepias, has a representative in the Colo- 

 rado desert, which produces numerous rush like, shining green stems, so 

 nearly devoid of leaves that they are only detected in narrow scale like 

 forms at the nodes. Several members of the Labiatae, nearly related 

 genera to Salvia, possess a similar- system of almost naked green stems. 



Drouth Resistant Root Systems. 



With this brief mention of the drouth resistant provisions of the stems 

 of plants, we should consider the arrangement of the roots. Actual desert 



