14 ROOT HABITS AND PARASITISM OF KRAMERIA CANESCENS. 



volcanic rock; below this was a layer of malpais mixed with lumps of cal- 

 iche; beneath the malpais-caliche stratum was one of hard caliche and vol- 

 canic rock. The two upper soil-layers are of about the same thickness. 

 The main root of Encelia was traced to a depth of 50 cm. and to a point 

 50 cm. distant from the axial line of the main root. Several laterals were 

 given off in the malpais soil-layer, within 20 cm. of the surface of the soil, 

 and extended as far from the parent axis as 1.5 meters. During" their 

 course the laterals remained in the malpais or the stratum beneath, and 

 did not attain a depth greater than 30 cm. 



One character only of the roots need be taken into account in the present 

 connection, and this relates to their branching habit. The large branches 

 of the roots are infrequent, but groups of filamentous roots are scattered 

 at short intervals, about 1 cm. apart, throughout their length. These root- 

 lets appear with the wetting - of the soil, at least in the summer season, and 

 fall away with its drying out. They, in fact, are deciduous, and play an 

 important part in the absorbing faculties of the plant. The association of 

 Krameria with the roots of Encelia takes place in the superficial soil-layers, 

 and often has a definite relation to the groups of the deciduous rootlets. 



The relative diameters of host and parasite roots, and the frequency of 

 the attachments of haustoria, were noted in several instances. Where 

 attacked, the host roots were from 2 to 5 mm. in diameter, and those of 

 the parasite were usually somewhat smaller, so that there is not the fairly 

 constant relation in size of host and parasite roots to be found in Covillea, 

 As illustrating" this point, it may be noted that a root of Encelia 5 mm. in 

 diameter was attacked by a root of the parasite only 1 mm. in diameter, 

 and other similar examples might be given. 



It seldom happens that only one attachment of a root of the parasite on 

 one root of the host occurs; usually there are more. In one instance 10 

 haustoria were attached to the host within a space of 7 cm., and again, 7 

 attachments were seen in a segment of root not more than 4.5 cm. in length. 

 The attachments are not necessarily from one and the same root of the 

 parasite, although frequently so, but may represent as many short branches 

 of one or more roots as there are haustoria; for example, one root of Kra- 

 vteria, 5.5 mm. in diameter, bore in less than 2 cm. 5 short branches, on 

 each of which was a haustorium 1.3 cm. or less from the base of the root. 



The point of penetration of the host root by the haustoria, wherever 

 observed, had a definite relation to the groups of adventitious roots above 

 described. Taking the case of the occurrence of 10 haustoria in 7 cm. , there 

 was 1 haustorium for each group of deciduous rootlets. The diameter of 

 the root of the parasite which bore the haustoria was 0.5 mm. or less, or the 

 size of the living adventitious rootlets. This observation, and other sim- 

 ilar ones, lead to the conclusion, where great differences in size lie between 

 the roots of parasite and host, that the attraction of the parasite roots ema- 



