260 



The Plant World. 



the rains for its appearance, and if they are abundant it may be 

 found in favorite places, as on the lower slopes of Tumamoc 

 hill, where the Desert Laboratory is situated, in large numbers. 

 The plant is gray-green in color and gives no hint either by its 

 aspect or its local distribution, of its parasitic nature. 



In the habitat of Orthocarpus, and growing at the same time, 

 may be found a large number of other plants, chiefly annuals. 

 Of these the following were seen to be the host plants: Astragalus 

 nuttallianus , Bigelovia hartwegii, Bowlesia lobata, Daucus pusillus 

 Delphinium scaposum, Eritrichium pterocaryium, Eschscholtzia 

 mexicana, Festuca octa flora, Gilia bigelovii, Lesquerella gordoni, 

 Lupinus sp, Mentzelia sp, Pectocarya linearis, Phacelia tanaeceti- 

 folium, Plantago jastigiata, Silene antirrhinum, Streptanthus 

 calijornicus, and Sysimbrium canescens. 



The typical root system of Orthocarpus may .be described 

 as having a well developed tap root and few laterals. Three 

 leading modifications of the root system were seen. These were 

 roots with short and coarse laterals, or those in which the later- 

 als were filamentous and either long or short, or, 

 finally, root systems in which the tap root is broken 

 up into three or more branches. While the immediate 

 causes which bring about these variations w T ere not studied, 

 they are thought to reside in part in the nature of the root system 

 of the host plant, which will be apparent from the following 

 brief account of some of the parasitic relationships. 



In association with Astragalus nuttallianus, Orthocarpus 

 has a prominent tap root with both long and short laterals. The 

 long branches of the tap-root are independent of neighboring 

 plants, but the short ones bear the haustoria. Both long and 

 short roots are rather coarse. In this case the length of the 

 haustoria-bearing roots is presumably dependent on the distance 

 by which the roots of parasite and host are separated, which, how- 

 ever, would not adequately account for the coarseness of the 

 roots of Orthocarpus. 



While growing in association with Festuca octaflora as host, 

 the roots of Orthocarpus are filamentous, and the root system is 

 poorly developed, On Eritrichium as host the roots of the 

 parasite are also filamentous, but they are very numerous In 



