32 ROOT HABITS OF DESERT PLANTS. 



No forms of roots other than that just sketched were seen in the field, but 

 dimorphic roots appeared in greenhouse cultures. Although this will be 

 referred to later, it will be well to describe these roots in this place. The 

 conditions under which the unusual form of roots occurred were as follows : 

 Among preliminary experiments, looking to a study of the aeration of 

 roots, was one which was arranged with two kinds of soils, namely, sand 

 from a wash and fine adobe clay (sifted) from the river bottoms. The bulbs 

 were planted, or were intended to be planted, on the line, which was a verti- 

 cal one, separating the two kinds of soil, but on removing the plants at the 

 end of the experiment one bulb was found to have been planted in sand 

 and the other in adobe, about i cm. in each instance from the opposite kind 

 of soil. The culture was running during a portion of November (1908) 

 and all of December, which was a rather cold period and unusually cloudy. 

 The green-house was not heated. 



When removed from the soil, the plant of the adobe side of the culture 

 had two leaves, 25 cm. long. The bulb had nearly or entirely disappeared 

 and in its place was the fleshy base of a stout root from the upper end of 

 which, or from the portion of the bulb remaining, was springing the usual 

 type of roots. The relation of the two is shown in plate 23. Of the 

 ordinary type of roots there were 13, which ranged from 2 to 11 cm. in 

 length and were wholly confined to the adobe side of the culture. The 

 central fleshy root was about 10 cm. long. It was i.i cm. in diameter at its 

 crown and narrowed rapidly as it approached the tip, which was attenuated. 

 The position occupied in the soil by the root was peculiar. In place of 

 going straight down — as did the root of the sand-grown plant — or of taking 

 a horizontal position, like the other secondary roots, it went downward but 

 at the same time inclined sharply away from the source of water supply, 

 and ended in a curl as shown by a figure of the plate. 



The plant on the sand side of the culture in certain particulars behaved in 

 a manner somewhat different from that described for its adobe-grown fellow. 

 The 2 leaves were 22.5 cm. long. The bulb was not resorbed, and from 

 it there sprang two sorts of roots, the relations of which are indicated in 

 plate 23. There were 7 rather coarse absorption roots, from i to 7 cm. 

 long, and a single fleshy root. All were of secondary origin ; the fleshy root, 

 however, as in the case of the plant described above, sprang from a point 

 on the bulb very near its base and went straight down from the bulb ; it 

 was 7.2 cm. long and 0.4 cm. in diameter at the crown. None of the roots 

 entered the adobe side of the culture. 



An explanation of the transformation of fibrous into fleshy roots of 

 Brodicea will not be attempted in this place. It may, however, be associated 

 with the unusually large amount of water available to the two plants rather 

 than to unfavorable conditions of aeration. A parallel instance, referred to 

 later, was observed in cultures of several arborescent cacti, inwhich the for- 

 mation of tuberous roots in species which do not normally produce tuberous 

 roots was induced in cultures conducted much as that just described. 



