16 ROOT HABITS ANB PARASITISM OF KRAMERIA CANESCENS. 



over 5 mm. in diameter, the haustorium had penetrated nearly to the cen- 

 ter and was wedge-shaped. Very plainly it had taken the place of one of 

 the medullary rays of the host, but whether it had encroached farther was 

 not determined. The haustorium had not extended in the cortex beyond 

 the place of its entrance into the central cylinder. The tissues of the haus- 

 toria examined did not show changes into percnanent tissue, as has been 

 noted occurs in Covillea. 



Franseria Dumosa. 



The habitat of Franceriadumosa, on the domain of the Desert Laboratory, 

 is on the eastward-sloping fans or bajadas which take their origin in the 

 Tucson Mountains west of Tumamoc Hill. The situation is an extremely 

 arid one. The upper soil-layer is about 20 cm. in thickness and is adobe; 

 beneath this is a mixture of adobe and caliche of about the same thick- 

 ness, and beneath the rotten caliche is either rock or hard caliche. 



The plants in the immediate vicinity of Franseria were Covillea tridentata, 

 Opuntia discata, Opuntia blakeana, and Parkinsonia microphylla, although 

 Franseria was the dominant plant. 



The roots of Franseria recall those of Covillea growing under similar 

 soil conditions. There is a main or tap root which goes down to the hard 

 caliche, which it penetrates if permitted by cracks in the caliche. Several 

 laterals arise within 12 cm. of the surface of the soil and reach out as far 

 as 1.6 meters from the central axis. These are confined to the two upper 

 strata, and mostly occur in the uppermost one, but may drop to the upper 

 surface of the hard caliche, on which they run for a considerable distance. 



The roots of Franseria are characterized by the abundance and luxuri- 

 ousness of groups of deciduous rootlets, which also were a prominent feature 

 of Encelia. 



It was only on the more superficial roots of Franseria, which were slen- 

 der, that the parasitic relations with Krameria were seen. The roots of 

 the host, where the union occurred, were less than 2 mm. in diameter, and 

 frequently equaled the parasite roots in size, as is indicated by plate 6. 



The material was not favorable for the exact study of the anatomy of 

 host and of parasite, so that the structural relation of the haustorium and 

 host and the destructiveness of the parasitism were not determined. 



Lycium Andersonii. 



The species of Lycium which occur in the vicinity of Tucson are to be 

 found on the flood-plain, sparingly on the slopes of Tumamoc Hill, or 

 wherever there is considerable depth of soil. The specimen of Lycium 

 andersoni on which Krameria was growing was found on the flats near 

 the wash west of the Desert Laboratory. 



The root-system of Lycium has not been especially studied, but it appears 

 to be of the generalized type; that is, the roots both penetrate the ground 

 deeply and extend away widely from the main-root axis. The shallow 



