12 ROOT HABITS AND PARASITISM OF KRAMERIA CANESCENS. 



4 meters from the main axis. In the main they ran in the adobe or in the 

 rotten caliche, but some extended beneath the rotten caliche to the hard 

 caliche and lay on its upper surface. 



A comparison of the root-system of Covillea from the slopes and of Kra- 

 meria will show at once how favorably the roots of Covillea are placed for 

 attack by those of the parasite. The roots of the two species, in fact, occupy 

 practically the same horizon, which is probably an important factor in 

 accounting- for the prevalence of Krameria on Covillea. But the relative 

 position of the species is unlike when plants from the fiat are considered, 

 for, as shown above, the roots of Covillea, like those of most other species in 

 the same habitat, strike deeply, while those of Krameria are more or less 

 superficial. 



Krameria is most frequently found in association with Covillea. The 

 parasitic relations of the two species were seen in rather small roots only, 

 and never in old ones, although remains of haustoria were found on the 

 older roots of the host. The figures in plate 2 show accurately the char- 

 acter of the roots of parasite and of host, and indicate relative size. 



In many instances the haustorium terminates the root of the parasite, 

 but this is not universal, since numerous attachments by sessile haustoria 

 have been seen at close intervals on the same root of the parasite. Fre- 

 quently the roots of host and parasite are of about the same size where 

 the union occurs, and probably of approximately equal age, although in 

 some instances the root of the parasite was smaller. 



Examinations were made of host roots which bore haustoria and which 

 were 1.5, 2, 7, and 9 mm. in diameter, and the general relation of haus- 

 toria and host and the relation of the tissues of the two species are indi- 

 cated by the semidiagrammatic figures which accompany this. 



Plate 2, fig. B, shows the attachment of the youngest haustorium seen 

 on Covillea. Penetration had already been effected through the cork and 

 the mechanical tissue of the cortex to the cambium and the woody portion 

 of the host root. In making the entrance to the wood the tip of the haus- 

 torium had followed a medullary ray. 



In older haustoria, such as shown in plate 3, figure 6, where the wo >dy 

 cylinder has been penetrated, the cortex of the host is encroached upon to 

 a marked degree, and the haustorium, in fact, extends both up and down 

 the root beyond the limits shown in the single sketch. The spreading of 

 the haustorium in the cortex, however, is always greatly restricted and 

 never reaches the extent of similar parts of the haustoria of the mistletoe. 

 (The anatomy of Phoradendron villosum, W. A. Cannon, Bull. Torr. Bot. 

 Club, 1901.) 



In the oldest specimens examined the apex of the haustorium ends bluntly, 

 whether it occupies only a small segment or half of the root (plate 3, fig. 7). 

 The outline of the haustorium in longitudinal section of the host is some- 

 what irregular, as shown by the figures. In one instance, where the 



