ROOT-SYSTEMS OF PERENNIALS. 77 



smaller plant was growing. It therefore appears that the root-system of 

 Dasylirion is essentially a comparatively superficial one. 



The shoot of Dasylirion functions as an important organ for food and 

 water storage, the storage apparatus being made up of the large central 

 axis and the enlarged leaf bases. The entire organ, in the larger plant 

 studied, was 25 X 30 cm. In another specimen, of which the stem axis 

 was 2 meters long, the water capacity would be very considerable, easily 

 comparable to that of the sahuaro. 



The root-systems of two specimens of Yucca were studied. Both of 

 these plants, although separated by some little distance, were growing 

 under practically identical soil conditions. The old specimens of Yucca, of 

 the type examined, have the habit of growing in colonies, to the exclusion 

 of plants of other species, but the younger forms occurred singly. 



The shoot of Yucca sp. was 70 cm. high and bore leaves 60 cm. in length. 

 The subterranean portion of the plant consisted of a branched tuber-like 

 root, from which arose several roots of the type characteristic of Dasylirion 

 and Agave, that is, coarse and little branched. The tuber measured 8 X 

 25 cm., and was richly supplied with sap. The branches of the tuber were 

 also fleshy, and three or four of them bore buds destined to produce shoots. 

 From the tuber 26 roots took their origin, wholly from the lower surface, 

 which were of two sorts, namely, immature, which did not function as 

 absorbing organs, and mature roots. The former were of a light pink color, 

 1.5 cm. in diameter and about 8 cm. in length, and were well filled with sap. 

 The older roots were dark red and generally shriveled ; they were unbranched 

 and were devoid of groups of filamentous roots, a characteristic of many 

 perennials of other families which were studied. The roots were variously 

 placed. The one penetrating deepest was traced to its end 1.23 meters 

 beneath the surface. Another, 1.22 meters in length, ran more or less hori- 

 zontally and reached 8, 12, and 22 cm. beneath the surface at different 

 points. It terminated abruptly. As compared with the root-system of 

 Dasylirion, that of Yucca sp. can be said to be poorly developed. 



The specimen of Yiicca radiosa studied had a shoot 64 cm. high and was 

 situated about 50 meters from the other species of Yucca just described. 

 It had a stout main root from which arose numerous laterals. The main 

 root was 5 cm. in diameter about 10 cm. beneath the surface of the ground 

 and expanded rapidly to a diameter of about 14 cm., which it maintained 

 almost to its end, 56 cm. below. The tip of the root was expanded and 

 divided into short forks. The entire root was thus 66 cm. in length and, 

 as it was well supplied with sap, it must be considered an important water 

 and food storing organ (plate 19, d, c). 



Laterals were given off from the main root from a point about 20 cm. 

 from the surface to the end of the root. They were all old and in appear- 

 ance were like those of the other species of Yucca. As in the other species, 

 they were comparatively close to the surface of the ground. 



