GENERAL FEATURES OP PARASITISM OF KRAMERIA. 21 



each other was like that of many other seedlings; that is, there was a long 

 tap-root which gave off near the crown several short and rather heavy lat- 

 erals. The laterals branched but little. An examination of the roots 

 under a microscope revealed, however, the absence of root-hairs. The 

 seedling Kramerias which grew in close relation to the Parkinsonia seed- 

 lings had root-systems of the same general character as plants grown 

 independently, differing only in certain details. Inspection of the roots 

 showed that there were two kinds of roots those terminated by a root -tip 

 having the usual appearance and those with tips which were enlarged. 

 Of the last form, seven were counted on one seedling, and one of these 

 was attached to a small root of Parkinsonia (fig. 9, plate 4). The others 

 were unattached, or if they had been attached to Parkinsonia roots the 

 union had been destroyed during the process of removing the roots from 

 the soil. In some instances th? latter explanation is the true one, as 

 scars of former attachments were seen in one or two of the swollen tips. 

 The haustorial structures terminating the roots of the parasite were not 

 formed until actual contact had been made with the roots of the host, and 

 this was brought about in a manner highly suggestive of chemotactic 

 stimulation, although no tests were made as to this matter. The haustoria 

 were seen to be modified root-tips in these cultures, although this does 

 not exclude the possibility of their lateral origin in other instances as new 

 organs. 



SUMMARIZATION OF GENERAL FEATURES OF PARASITISM OF KRAMERIA. 



The center of interest in the study of the parasitism of Krameria lies 

 in the demonstration that a well-known genus, supposed to be composed 

 entirely of autotrophic species, contains forms which are habitual parasites, 

 presenting many novel morphological features. 



Several species have been used in Europe for commercial purposes for 

 over a century. The genus, also, was represented early in the preceding 

 century in the gardens of Kew. It is therefore somewhat strange that 

 the fact of parasitism in Krameria should remain undiscovered for so long 

 a period. Further investigation is necessary to determine whether para- 

 sitism is a characteristic of the genus or w r hether it is only exhibited by 

 two of the three species of Krameria found in the vicinity of Tucson. 



The seed of Krameria canescens, whether sown during the season of 

 their maturing or a year later, germinate readily, irrespective of the pres- 

 ence or absence of the host plant. 



The seedling Krameria, in common with the seedlings of other para- 

 sites, is independent for an undetermined period. It does not form root- 

 hairs. The root-systems of the mature plant possess certain habital 

 features which distinguish them from those of autotrophic plants. For 

 example, the members of the adult root-system are shallowly placed, 



