22 ROOT HABITS AND PARASITISM OF KRAMERIA CANESCENS. 



although the species does not form water-storage organs and although the 

 soil conditions may be suitable for deep penetration. Such adult systems 

 generally include the remains of a prominent tap-root. This organ has 

 not been seen in a functional condition. The shoot of Krameria is chloro- 

 phyllose and bears narrow, inconspicuous leaves during the rainy seasons. 

 The manner of the formation of the haustoria, as well as the morpho- 

 logical character, appear to be unlike in young and in old plants, but this 

 has not been actually proved. In seedlings the haustoria terminate the 

 roots; in established plants they appear to be lateral. 



The haustoria do not appear on seedlings which are growing indepen- 

 dently of other species, but if other plants, possible hosts, are associated 

 with the young plants of Krameria, haustoria are formed freely, and appa- 

 rently without direct contact with the host. 



In the young" plants the attachment of the haustoria takes place imme- 

 diately back of the tip, in the region of the root-hairs of the host. Although 

 apparently different, the association of the roots of host and parasite of 

 older plants may be similar to that in the seedling, even if this is not the 

 sole manner of bringing about the attachment. Reference is here made 

 to occurrences seen in the parasitism of Krameria canescens on Franseria 

 dumosa. In this host there are organized on the old roots, at intervals of 

 about 1 cm., groups of rootlets which are functional only during and for a 

 short time after moist seasons, and which arc developed as a result of fav- 

 orable moisture conditions of the soil. Where the parasite's roots are placed 

 near host roots bearing these deciduous rootlets haustorial attachments 

 are found at places which correspond to the places of origin of such decid- 

 uous roots. It would appear that the union would first be formed with 

 the deciduous roots, from which access would be gained to the older and 

 permanent host root. 



In addition to the penetration of very young roots of the host by haus- 

 toria terminating the very young roots of the parasite, observations on 

 Prosopis velutina as host indicate that penetration may also take place in 

 older host roots by haustoria which are lateral in origin. 



The earliest stages in the union of parasite and host were not seen. The 

 youngest haustoria in the material studied had already passed through the 

 cortex of the host root and its tip was resting against the periphery of the 

 woody cylinder. In going through the cortex, or ramifying in it, the 

 sucker appears to follow the lines of least resistance, but the portion of 

 the cortex finally occupied is never large. 



The mature haustorium does not penetrate the host root to a great depth; 

 in fact, it has not been observed more deeply than 2.5 mm. in the woody 

 cylinder. The portion of the haustorium which is in the wood of the host 

 does not (as in the mistletoes, for instance) conform to the medullary 

 rays in form or in spacing, but is blunt in longitudinal section, and not 

 wedge-shaped as in the other parasites. In extreme cases the haustorium 



