ROOT HABITS OF DESKRT PLANTS. 37 



Parasitism of the plant has been observed on the foHowing species : 



Astragalus nuttallianiis. Eschscholtzia mexicana. Pectocarya linearis. 



Bigelowia hartwegii. Festuca octoflora. Phacelia tanacetifolium. 



Bowlesia lobata. Gilia bigelowii. Plantago fastigiata. 



Daucus pusillus. Lesquerella gordoni. Silene antirrhinum. 



Delphinium scaposum. Lupinus sp. Streptanthus californicus. 



Eritrichiumpterocaryum. Mentzelia albicaulis. Sisymbrium canescens. 



The typical root-system of Orthocarpus may be described as consisting 

 of well-developed tap root and few laterals, but greater variation in the 

 character of the root-system of this species was seen than was observed 

 in that of any other annual. Three leading modifications of the roots 

 were seen. These were: (i) roots with short and coarse laterals; (2) those 

 in which the laterals were filamentous and either long or short; (3) root- 

 systems in which the tap root is broken up into three or more forks. 



While the immediate causes of these variations were not investigated, 

 it is thought that they may be connected with the nature of the root- 

 system of the host plant, as will seem probable from the following. 



In association with Astragalus, Orthocarpus has a prominent tap root 

 with both long and short laterals which are rather coarse. The long lat- 

 erals are independent of the host plant, but the short ones bear haustoria. 

 In the case of the length of the laterals, it is presumably directly dependent 

 on the distance by which the parasite and the host are separated, which, 

 however, would not account for the coarseness of the roots of the parasite. 



When growing in association with Festuca octoflora as the host, the roots 

 of Orthocarpus are filamentous and the root-system is poorly developed. 

 On Eritrichium the roots of the parasite are also filamentous, but very 

 numerous. In connection with Silene, the main root of Orthocarpus is 

 broken up into several relatively large roots and the laterals are very few. 



Whatever may be found to be the chief causes in bringing about the 

 modifications in the character of the root-system of Orthocarpus, as described 

 above, it is of interest to note that the soil conditions were as uniform as 

 one would expect to find in a single habitat, and that the root-systems of 

 the host plants had specific differences which the roots of the parasite to a 

 degree reflected. Thus the roots of Astragalus are coarse and those of 

 Eritrichium are filamentous, and the roots of Orthocarpus when attached to 

 these plants are coarse or fine, as the case may be. Whether Orthocarpus 

 can live independently is not known, so what its root-system would be 

 as an independent plant can not at present be told. However greatly 

 Orthocarpus changes the character of its root-system with differences in 

 the roots of its hosts, it does not modify its life-cycle if that of the host 

 chances not to coincide with that of its own. When associated with 

 annuals, the plant would naturally not be influenced to prolong its period 

 of existence, and when connected with a perennial, as with Bigelowia, it 

 appears not to do so (plate 7). 



