VVALDRON— THE PEANUT 321 



They were, however, very short and comparatively few in number. 

 It was noted, however, with some surprise, that on the roots of 

 nearly every plant, tufts or whorls of hairs were present as rosettes 

 at the base of some of the side rootlets. These were much longer 

 than the first-mentioned type, as is set forth in the figure. The 

 possibility that the influence of potting may have in some way 

 caused the development of these rosettes as well as tip hairs, led to 

 an examination of the roots in the center of pots, and of roots on 

 plants which had been carried forward in boxes (2x3x1^ ft.) 

 Such roots have less air drainage than those along the inside wall 

 of a flower pot. Plants were removed, their roots carefully washed 

 out, and tufts of hairs were found at the base of many newly formed 

 side roots. 



The presence of normally produced tip hairs was carefully watched 

 for, but none was found. The only plant mentioned which had these 

 was one, the roots of which were in a moist air compartment, formed 

 by the drainage hole of the bottom of the flower pot, the broken 

 crocks just above, and the cinder bench below. This suggests, 

 therefore, that optimum oxygenation is a necessary factor for the 

 tip hair growth. None were found on the roots of any plants in the 

 soil, either under dry or moist conditions. Since the plant seemed 

 to have at least a hereditary tendency under certain conditions 

 to produce these normal tip hairs it was considered worth while to 

 determine, if possible, the exact causes or stimuli which affect their 

 growth and that of the rosette type. Observations and experi- 

 ments were, therefore, carried on with this in view, as well as to 

 determine the causes and method of production of, and differences 

 between, the two forms. The results of this investigation are de- 

 scribed in succession to the following discussion of the works of 

 others on this subject. 



Concerning the presence and absence of root hairs, Strasburger 

 states that in some few instances as in some conifers plants bear no 

 root hairs. Jost"' says that few plants produce none, probably re- 

 ferring to aquatic types. Haberlandt" refers to two stages in the 

 specialization of absorptive tissue in plants, (i) Some plants are 

 content to increase their absorptive surface by a greater output of 

 side roots, the epidermal cells of which are flat or slightly convex in 

 their outer walls. But he states that this type includes marsh and 

 aquatic plants, and is less advanced in this regard. If this is a stage 

 in specialization, would it not be possible to think of it as a reduc- 



