MENODORA SCABKA; PARKINSONIA MICROPHVLLA. 17 



roots are placed largely within 20 cm. of the surface of the ground. It 

 was to these more superficial roots that those of the parasite were attached. 



The soil at the place in which the attachments were studied was clay 

 with an admixture of rather coarse sand and was more than 2 meters deep. 

 The plants which occurred near Lycium and Krameria were those charac- 

 teristic of the flat, that is, . Uaciaconstricta, Covillea tridentata, Ephedra anti- 

 syphilitica, Parkinsonia torreyana, Prosopis velutina, Zizyphus parryi, and 

 others . 



Roots of Lycium varying in diameter from 0.5 to 5.0 mm. were seen to 

 bear haustoria, while the roots of the host were slightly larger than this. 

 It frequently happened that roots of about equal size were found united, 

 although host roots as large as 5 mm. bore roots of Krameria no larger 

 than 1 mm. 



The structural relations of host and parasite were not examined, but the 

 frequency and nature of the attachment lead to the conclusion that the 

 relationship must be a damaging' one to Lycium. 



Menodora Scabra. 



The specimen of Menodora upon which Krameria canescens was found 

 parasitic was growing on the flats immediately west of Tumamoc Hill, not 

 far from the specimens of Acacia constricta, Ephedra antisyphilitica , Prosopis 

 velutina, and Zizyphus parryi, on which the parasitism of Krameria was also 

 demonstrated. 



Menodora is a small shrub, usually under 50 cm. high. In the vicinity of 

 the Desert Laboratory it never occurs in large numbers in any locality, 

 but is more or less scattered. 



Krameria was seen attached to a root 2 mm. in diameter (plate 4, fig. 4) 

 in which the haustorium had penetrated to the wood of the host root. 

 The detail of the structural relationship of host and parasite, the destruc- 

 tiveness of the parasite, or the frequency of its attack on the host were not 

 investigated. 



Parkinsonia Microphylla. 



This species occurs on the dry, well-drained slopes above washes in 

 the vicinity of the Desert Laboratory and on the slopes of the low moun- 

 tain. It is an intense xerophyte. Its leaves are minute and are kept only 

 during" the rainy season and for a short period afterward, so that for the 

 most of the year the tree is without foliar surfaces. The rate of transpi- 

 ration of Parkinsonia, when in full leaf, is considerable, but is extremely 

 low when the leaves have gone. On account of the last fact, Parkinsonia 

 would not be considered, a priori, a favorable host for a seed-parasite. It 

 may be mentioned in this connection that it is not unusual for the mistletoe 

 on desert trees to perish during dry seasons from water-famine, though 

 the host may survive. 



