root habits of desert plants. 29 



Pectis Prostrata. 

 The specimens of Pectis studied were growing on Tumamoc Hill near the 

 Laboratory building. They were from 7 to 12 cm. in length and in flower. 

 The general habit of the plant is shown in plate 4. The main root is very 

 delicate and bears several long laterals within 3 cm. of the surface of the 

 ground. The longest of these were over 13 cm. and bore numerous branches, 

 which also were branched. The root-system as a whole may be character- 

 ized as being little branched, the laterals of all orders are relatively few, 

 and composed of delicate roots only. 



SOI.ANUM El^AGNIFOLIUM. 



Immature plants of Solannm were collected August 22, of which one had 

 a shoot 6 cm. high and bore several large leaves. A tap root dominated the 

 root-system ; it was traced over 15 cm. Laterals were given off at occasional 

 intervals along as much of the main root as was examined, but they were 

 mainly confined to the upper 4 cm. The laterals of the first order are fine 

 and bear filamentous branches. There are also roots of the third order 

 present. The roots arise singly; there are no rudiments. The leading char- 

 acteristics of the root-system are the rather stout tap root and the delicate 

 laterals, with no roots of intermediate diameter between (plate 4). 



Trianthema Portulacastrum. 

 The specimens of Trianthema which were studied were collected on the 

 western edge of the Santa Cruz flood-plain, August 26. The shoot of the 

 plant to be described was about 1 7 cm. high and bore 9 branches and num- 

 erous large leaves, and therefore possessed a large transpiration surface. 

 The root-system is characterized by a preponderance of coarse roots. 

 The tap root is 3 mm. in diameter at the crown, is over 15 cm. long, and 

 bears (within 4 to 5 cm. of the surface of the ground) 5 prominent laterals, 

 the longest of which was more than 17 cm. At intervals of about i cm. the 

 laterals of the first order bore short filamentous roots and rudiments of 

 roots. The number of rudiments is large, a feature which distinguishes 

 this plant from nearly every other one examined. The rudiments appear 

 as faint dots along the laterals in plate 5. 



ViCIA SP. 



The specimen of Vicia whose roots were examined was growing near the 

 Laboratory and was collected August 10. The shoot of the plant was 

 mature and bore fruit and flowers. The specimen studied bore 7 branches 

 and numerous linear leaves. The root-sj-stem is characterized by a prom- 

 inent tap root, which was 2 mm. in diameter at the crown and over 20 cm. 

 long, and large laterals arising rather far beneath the surface of the ground. 

 A portion of the laterals of the first order are in .groups of 2 or 3, although 

 they mainly arise singly. The laterals branch but little and leave the 

 impression that the absorption system of the plant is a rather meager one. 

 A few tubercles are borne on the larger laterals. 



