28 root habits of desert plants. 



Dysoda Papposa. 

 Specimens of Dysoda in flower were procured August 26. The shoots 

 were 12 to 15 cm. in length, much branched, and well covered with leaves. 

 The tap root dominates the root-system. This evidently reaches deep, 

 although unfortunately but 10 cm. of the root was uncovered. The laterals 

 are filamentous and are given off from the main root somewhat farther 

 from the surface of the ground than is usually the case in summer annuals. 

 The laterals of the first order bear branches and these also are branched, 

 but the entire extent of the filamentous roots is relativel)' slight (plate 4). 



Euphorbia Glyptosperma. 

 Euphorbia glyptospcnna is most abundant on Tumamoc Hill, where the 

 specimens examined were collected August 26, but, like most of the other 

 annuals it also occurs in the other habitats in the vicinity of the Laboratory. 

 The specimens studied were about 7 cm. high, much branched, with a large 

 leaf surface, and in flower. The roots grade in diameter from the main root, 

 which is somewhat over i mm. in diameter at the crown, to the ultimate 

 filamentous ones, although as a whole the roots are relatively coarse. The 

 laterals of the first order arise for the most part within 3 cm. of the surface 

 of the ground. They occur singly; no rudimentary roots were observed. 



Kallstrcemia Grandielora. 



Kallstramia is one of the less abundant but most striking of the summer 

 annuals. It is of a semiprostrate habit, which varies with its stage of 

 growth or with the conditions under which it has developed. If the summer 

 rains are slight, so that the period of growth of the plant is short, its habit 

 is nearlv upright, but should the stormy season be prolonged, or should 

 rains occur after those of early summer have passed, and before the plant 

 dies, growth is renewed if the latter is the case, or in the former case growth 

 is so active that the plant becomes vine-like and prostrate. Under such 

 favorable circumstances it may cover as much as 16 square meters of 

 surface, and perhaps even more than this. The plants whose roots were 

 removed either were young or had attained the first stage of growth de- 

 scribed above, that is, they were upright and mature. 



The plant to be described was collected on Tumamoc Hill on August 10. 

 The shoot consisted of two branches and several compound leaves and more 

 numerous flower buds. It was 27 cm. long. 



The root-system consists of a main root, with a relatively stout crown, 

 and one long and one short branch, together with slender laterals, which 

 are mainly close to the surface of the ground, and their proper branches. 

 The longest lateral is over 21 cm. in length and bears two branches over 10 

 cm. each. Most of the laterals of the first order and all of the higher orders 

 are filamentous. The main root penetrated the ground more than 22 cm. 



The leading features of the root-system, which is a rather extensive one, 

 are shown in plate 4, 



