ENCELIA FARINOSA. 13 



haustorium had penetrated the wood to a depth of 1 mm. , a tongue of a few 

 cells was put out from its tip and extended a small way into and with the 

 grain of the wood, that is, parallel to the course of the ducts of the host. 

 Between such a tongue and the main body of the haustorium there ex- 

 tended for a short way into the haustorium a few strands of the ducts of 

 the host, and at the tips of these strands were joined to it pitted haustorial 

 cells, which in turn united with the distal ends of the ducts of the haus- 

 torium. In this manner the water-conduction system of host and of parasite 

 was made continuous. Conditions analogous to this, but just beginning, 

 were seen also at various places along the apex of the haustorium; that is, 

 tongues of the haustorium, of few cells only, were extended into the woody 

 cylinder, parallel to the course of its ducts, and usually always between 

 them. The tongues perhaps always followed the medullary rays, or at 

 least the wood parenchyma of the host. But in these cases the distal 

 haustorial cells were not yet pitted, or at least had not yet lost their con- 

 tents, although they may have lost their function as epithelial cells. 



The peripheral cells of the distal end of the young haiistorium, as men- 

 tioned in another place, have the appearance, and evidently the function, 

 of epithelial cells, but with the maturing of the haustorium, as shown in 

 the preceding paragraph, these change their function and their essential 

 structure. This change is not inevitable, however, and we may find an 

 old haustorium with thin-walled cells in the tip, which unquestionably 

 have retained their primitive function. 



The extension, if not the penetration also, of the parasite in the tissues 

 of the host takes place after or with their breaking down, probably through 

 solvents secreted by the epithelial cells of the haustorium. These tissues 

 include the cellulose of the cortical parenchyma and the lignified mechan- 

 ical tissue of the cortex, as well as the tissues of the woody cylinder. The 

 evidence that lignified tissues are dissolved is based on two facts, of which 

 the first is the entire absence of such tissues in the haustorium and the 

 observation of partly digested lignified cortical cells adjoining the secret- 

 ing haustorial cells. Were the lignified cortical cells of the host simply 

 engulfed, as may happen in the mistletoes, they might be detected within the 



haustorium. 



Encelia Farinosa. 



Encelia is a shrub with a very limited local distribution. It is abundant 

 only on the southern, the eastern, and the western exposures of Tumamoc 

 Hill . Its distribution agrees, therefore, very well with that of the sahuaro. 

 Encelia occurs sparingly on the northern slope, and its association with 

 Krameria was observed here as well as on the western slope. 



The root-system of Encelia is a generalized one, whose depth extension 

 is determined by the character of the ground. At the place where the plant 

 which was studied was growing the soil conditions were as follows: The 

 uppermost 20 cm. was malpais, that is, a finely divided soil derived from 



