20 ROOT HABITS AND PARASITISM OF KRAMERIA CANESCENS. 



the root-system firmly fixed. In these regards it is the antithesis of Covil- 

 lea, which has a plastic root-system and cosmopolitan habit. 



The roots of Zizyphiis to which haustoria were attached were the most 

 superficially placed ones of the plant. Haustoria were found only on large 

 roots, namely, those from 5 mm. to 2 cm. in diameter, and not on small 

 roots, a condition not before met with in the studj . The relative size of 

 host root and of parasite root in Zizyphus is also unlike that observed so con- 

 sistently between host and parasite in other nutritive couples, in that the 

 host root appeared always to be larger. A few measurements will illus- 

 trate the point. A root of Zisyphus 2 cm. in diameter bore several haus- 

 toria whose diameter was less than 5 mm. A root of the parasite 2.5 mm. 

 in diameter was seen attached to a root of the host 1 cm. in diameter, and 

 another host root 5 mm. in diameter was attacked by a root of Krameria 

 whose diameter was only 2.5 mm. 



An examination was made of a parasitic union in which the host root 

 was 5 mm. in diameter (fig. 8, plate 4). It was seen that the haustorium 

 had penetrated well into the woody cylinder and into the cortex of the 

 host, but its tissues were disorganized and it was apparently lifeless, as 

 was the case in several other specimens examined. The cause of the dying 

 of the tissues of the haustorium was not inquired into; it may, however, have 

 merely been insufficient water-supply, as was noted above under the dis- 

 cussion of the parasitism of Krameria on Parkinsonia microphylla, and as 

 occasionally occurs among the mistletoes. But in the case of the Krameria 

 the plant as a whole was living and did not exhibit outward signs of the 

 death of the haustoria. 



CULTURES OF KRAMERIA CANESCENS. 



Early in the spring' of 1909 some seeds of Krameria canescens which had 

 remained from the crop of the preceding summer were planted in pots in 

 the greenhouse at the Desert Laboratory. A portion of the seeds were 

 sown by themselves, that is, without other seed, and a portion were sown 

 together with seed of Parkinsonia aculeata. In the course of a few days 

 seedlings of both species of plants appeared at about the same time. Kra- 

 meria seedlings, whether near or remote from the proposed host, grew 

 equally well, so far as observation could determine; neither grew so rap- 

 idly as the seedling Parkinsonias. With the advent of warm weather in 

 April the pots were removed from the greenhouse to the lath shelter near 

 the rear of the building, and on May 7 the cultures were taken up with 

 great care and the young plants preserved in a solution of formalin for 

 later study. 



The seedling Kramerias, whether in association with the seedling Park- 

 insonias or separated from them, were indistinguishable as to shoots, but 

 an examination of the roots of the plants revealed differences. The root- 

 system of the specimens which grew isolated from Parkinsonia and from 



