EXPERIMENTAL CULTURES. 



85 



w 



to possess them, but they were not to be found in a few, and in one species 

 their formation could not be induced experimentally. In Amsinckia spec- 

 tabilis, these rootlets arc present as rudiments, whatever may have been 

 the water conditions, but are only brought to full development under favor- 

 able moisture relations; while in Rafinesquia, as stated above, no adventi- 

 tious rootlets were seen in nature and none could be induced to form in 

 experiments. The cultures were carried on in the plant house where the 

 temperatures were higher than out of doors. (See page 40). 



In December-February, 1907-8, a culture was set for the purpose of seeing 

 the relative extent of the roots of a typical desert seedling and those of 

 a pronounced mesophyte. The seeds planted were of the garden water- 

 melon and of Fouquicria spJendcns. When the plants w^ere taken up the 



shoots of each species were about of a 

 height, although the transpiring sur- 

 face of the water-melon, naturally, 

 was much greater. The root-system 

 of the seedlings of the two species was 

 found to be very unlike; that of the 

 water-melon was three to four times 

 as long as the shoot and bore very 

 many laterals of the first order, while 

 that of the Fouquicria was only about 

 as long as the shoot and bore few lat- 

 erals. The relative development of 

 the two is imperfectly shown in plate 

 22. The behavior of the roots of Fou- 

 quieria brought about the starting of 

 for the purpose of 

 learning the direction which the tap 

 root of a typical desert plant would take if provided with an abundance of 

 water. Water poles of porous clay tubes were placed in opposite ends of 

 a box and, after the soil moisture coming from the poles had reached an 

 equilibrum throughout the box, seeds of water-melon and of Parkinsonia 

 aculeata were sown at different distances from the centers of water supply 

 (fig. 17). The root of the water-melon went straight down, while that of 

 Parkinsonia inclined away from the water pole in a marked manner. The 

 difference in reaction of the roots of the two plants is thus a striking one, 

 whether the immediate cause is too much water or too little oxygen, or 

 other causes not now suspected. 



This form of culture was later repeated using bulbs of Brodicea capitata 

 in place of the other plants previously used, with the distribution of water 

 from porous clay cups, of the kind employed by Livingston, arranged as 

 before, but with fine and coarse earth arranged in alternating vertical col- 

 umns. Bulbs were placed both in the fine soil and in the coarse, and on 



Fig. 17. — Culture of water-melon (1) and 



Fouquicria splcndetis (2jin a soil kept con- aUOthcr CUltUrC 

 stantly moist by a porous clay cup shown 

 at left. 



