ROOT-SVSTEMS OF PERKXXIALS. 



75 



1.44 meters deep. Like the root-systems of the other plants, this one also 

 comprised several laterals which were borne about 15 cm. from the surface 

 of the soil and which reached about 90 cm., but then, turning sharply, ran 

 directly downward to an undetermined depth. The slender roots, so 

 numerous on the last plant examined, were also a feature of this one. 



Dasylirion Texanum, Yucca Radiosa, Yucca sp., axd Agave sp. 



Up to this point the plants of the bajada, which have been described, 

 grew in the immediate neighborhood of the Desert Laboratory, or at most 

 not more than a mile distant, but the plants selected for the purpose of 

 examining types other than had been seen heretofore, were found in the 

 region west of the Rincon mountains, about 20 miles east of Tucson. The 

 bajada at that point was perhaps 4 miles from the base of the main range 

 of the mountains and at an elevation approximating 3,600 feet, or about 

 1,300 feet higher than Tucson. The greater altitude means lower tempera- 

 tures and greater rainfall, although, as there are no records of the locality, 

 the extent of the difference from Tucson in these regards is not known. 



The soil conditions 

 varied where the plants 

 studied were growing. 

 At the Yucca sp. habitat 

 the upper soil, for more 

 than a meter, was sand 

 and red clay with caliche 

 underlying, while in the 

 habitat of Yucca radiosa 

 and Dasylirion texanum 

 the upper soil, although 

 of like character, was 

 only about 20 cm. in 

 thickness. The two 

 plants first named were 

 50 meters apart, and 

 were about 200 meters 

 from Dasylirion. The Agave sp. was found on the upper bajada slope near 

 the base of an outlying range approximately 2,000 meters south of the 

 other plants. The soil was similar to that above described, except that 

 there was a larger amount of sand and rocks. 



In the immediate vicinity of the Agave studied were observed Calliandra 

 sp., Encelia jarinosa, Foiiquieria splendens, Hyptis sp., Opiintia blakeana, 

 and Parkinsonia micro pJiylla. Of the two specimens of Agave examined, 

 one was about 20 cm. high and the other somewhat larger. The roots of 

 young agaves, and of the older ones as well, were borne in a cluster at the 

 base of the shoot. All of the roots were of about equal length and very 



4. — a. \'crtical extension of root-system of 'i'ucca 

 radiosa from the bajada near Rincon mountains. Dotted 

 line indicates boundary between adobe upper soil and 

 underlying rotten caliche. 

 Vertical extension of root-system of Yucca sp. from the 

 bajada near the Rincons. 



