8 ROOT HABITS AND PARASITISM OF KRAMERIA CANESCENS. 



many points of attachment of ^he roots of the two plants were observed, 

 and comparative study showed that Covillea is the favorite host of the 

 parasite. 



ANATOMY OF THE ROOTS. 



The roots of Kramer ia branch little, they are smooth, and are dark red 

 in color, due to pigment in the cells of the cork. They are mechanically 

 very weak. The cortex is characterized by a well-developed cork and by 

 the total (?) absence of mechanical tissue. The sieve-tubes of the phloem 

 were not demonstrated, although repeated attempts were made with the 

 usual reagents. It is not supposed, however, that sieve-tubes are not to 

 be found in the cortex, but this may be attributable to the apparently 

 dormant condition of the roots, since they were collected during the dry 

 foresummer season. In the woody cylinder the vessels and the tracheae are 

 large and the medullary rays are not well marked. Between the vessels 

 are wood parenchyma and medullary-ray cells No wood fibers were seen. 



In places the roots of Krameria flatten and form cushions of tissue in 

 contact with the host, and haustoria arise from these cushions. These 

 haustorial cushions were seen to be terminal in a culture in which Parkin- 

 sonia aculeata was host, but in other instances, particularly those in which 

 Prosopis velutina was the host, the root was seen to be extended with as 

 many as 7 cushions on a section of the root of the parasite not more than 

 7 cm. in length. In some instances it appeared that the cushions had been 

 formed laterally to an extending root, while in others the cushions were 

 terminal and the extension of the root was accomplished by development 

 of a branch back of the haustorial cushion. 



THE HAUSTORIUM. 



The haustorium consists of two portions, a part exterior to the host, 

 the haustorial cushion, and a part within the host, which corresponds to 

 the "sinker" in the mistletoe (fig. 1, plate 3). A longitudinal section of 

 an haustorium 8 mm. in diameter has the following general structure: 

 The immature haustorial cushion is composed of a covering of cork, and 

 within parenchyma which is undifferentiated save as to form. The par- 

 enchyma is divided into cortical parenchyma and that of the central cyl- 

 inder. The long diameter of the cells compt^sing the former tissue, that 

 is, the cortex, is transverse to the main axis of the haustorium, while the 

 axial parenchymatous cells are cuboid. The cortical cells thus have the 

 appearance of having been pulled laterally as the cushion flattened; but 

 subsequently they regain their primitive' cuboid form, and, as will soon 

 be seen, even become so greatly changed that the greatest longitudinal 

 diameter coincides with the long axis of the haust(>rium. The tissues here 

 described do not make up the whole of the cushion, but only about two- 

 thirds of the lower, that is, the distal portion of it. The upper or proxi- 

 mal portion of the cushion is composed of an outer cork and an inner mass 

 of undifferentiated cells, which remain undiiferentiated and constitute a 



