GENERAL FEATURES OF PARASITISM OF KRAMRRIA. 23 



comprises half of the cross-section, the portion of the host being semicir- 

 cular merely. 



The haustorial branch is composed of three regions the root proper, 

 the pear-shaped cushion which rests against the host, and the sucker. Of 

 these regions the structure of the last two is peculiar and bears no resem- 

 blance to the structure of the former, that is, to a root. Penetration may 

 be affected before the haustorial tissues are differentiated, although the 

 three regions above mentioned may be made out at a very early stage. 



Vascular strands of the sucker unite with the conductive system of host, 

 but it is doubtful whether the phloem of host and parasite are continuous. 



The duration of the parasitic relation was not learned, but it may be 

 inferred from the nature of the changes which occur in the tissues of the 

 haustorium. In most instances the tip of the sucker is composed of thin- 

 walled cells which may or may not have a secretory function, and no per- 

 manent tissue besides a few strands of vessels in the haustorium. In 

 Covillea only, as host, were old haustoria seen which had a portion of the 

 fundamental tissues of the sucker changed into non-living cells. Such 

 histological facts agree very well with the observations that haustoria are 

 most frequently found on young host roots and are usually small, and sug'- 

 gest the probability that the haustoria become quiescent early and that 

 they have a limited functional existence. 



Various protective reactions appear in the host after the attachment has 

 been formed, although the decadence of the haustoria is frequently to be 

 traced to an insufficient supply of water. In Parkinsonia microphylla as 

 host the portion of the conductive system of the host which was contiguous 

 to the sucker was plugged, although the portion more remote was open and 

 functional. In this case the haustorium had organized cork in all save a 

 very limited area in the cortical portion of the host root. 



In some points the haustoria of Krameria are unlike those of certain 

 other hemiparasites which have been closely studied. In Melampyrum 

 ftratense, whose physiological characteristics until recently have been in 

 doubt, the haustoria arise laterally and never terminate the roots. (M. 

 Gautier, Sur le parasitisme du Melampyrum pratense. Rev. Gen. Bot., 

 Feb., 1908.) This is also true of the origin of the haustoria in Santalum 

 album, which has been investigated by Barber. (Studies in Root Parasit- 

 ism: The Haustorium of Santalum album. Mem. Dept. Agric. India, Bot. 

 Ser. , vol. 1., No. 1, 1906.) In the seedling Krameria canescens, however, 

 the haustoria are root-tips which have taken on the new function. That 

 this is not the only method of haustorial formation in the parasite, how- 

 ever, is likely, since in the parasitism of Krameria on Prosopis velutina 

 they were probably lateral. In the latter case young haustoria were seen 

 on freshly formed branches of old Krameria roots. It is therefore probable 

 that the method of the organization of the haustoria in Krameria is not an 

 invariable one. 



