THE ROOT HABITS AND PARASITISM OF KRAMERIA 



CANESCENS GRAY. 



By W. A. Cannon. 



PARASITIC SEED-PLANTS OF THE DESERT. 



Three genera, comprising' half a dozen species, of semiparasitic seed- 

 plants are to be found on the domain of the Desert Laboratory. These 

 include Phoradendron, Orthocarpus, and Krameria, of which parasitism in 

 the last two has been recently discovered. 



Phoradendron is represented here by P. calif "ornicum, a leafless form, 

 which occurs on Prosopis velutina, Parkinsonia torreyana, and Acacia con- 

 strirta, among the trees, and it is said to be attached to Covillea tridentata 

 and Zizyphus parry 7, of the shrubs. The broad-leaved form P. villosum 

 is common in the neighboring river-bottom, where it attacks the native 

 ash and poplar. 



Ort/wcarpus purpurascens is an annual which appears in the spring if the 

 rains have been sufficient to bring out the annuals peculiar to this time of 

 the year. If the rains fail, or are insufficient in amount, OrthocarPus is not 

 to be found. In the spring of 1908 the annuals were especially abundant, 

 and among them Orthocarpus, and a very favorable opportunity was given 

 for the study of the parasite. The observations then made showed that 

 Orthocarpus was parasitic on 18 species, all but two of which were annuals. 

 (W. A. Cannon, Parasitism of Orthocarpus purpurascens, Plant World, xn, 

 259, 1909.) 



The third genus of parasitic seed -plants has been found to be one of 

 the most striking and interesting of all those observed. Krameria is one 

 of the most common of the desert shrubs, with no outward indication of its 

 parasitic nature. It usually occurs near another species, but not in so 

 close proximity as to attract special attention. Krameria is less than a 

 meter high, much branched, and bears small leaves. It produces flowers 

 in summer and fruits abundantly. The general habit of the plant is shown 

 in plate 1. 



KRAMERIA CANESCENS AND SOME FEATURES OF THE KRAMERIAS. 



The genus Krameria (Krameriaceae) was formerly included among the 

 Polygalacese and the Leguminosae, and has no close affinities with other 

 parasitic seed-plants. It is an American genus of about 13 species and 

 extends from the warmer portions of North America to Chili, but is most 

 largely represented in Mexico. (Englerand Prantl, Pflanzenfamilien, in, 

 3, p. 167.) It is best known for its commercial value. Roots of certain 

 species of Krameria have been shipped to Europe since 1796, where they 



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