1% The Plant World. 



under my observation within a radius of 75 miles of Tucson, 

 and have seen only two dead trees of full size. 



I have found that the shade of adult trees and other large 

 plants does not materially lessen the death rate, for the condi- 

 tions of soil and atmospheric aridity are just as pronounced on 

 the north side of trees and shrubs during the arid fore-summer 

 as they are in other situations. I have not found that there is 

 any importance in the number of seedlings occupying the same 

 spot, as respects their chances of survival. There are several 

 cases among the seedlings of 1910 in which two and three indi- 

 viduals growing as close together as possible have all survived to 

 date, and on a single square metre w ith a population of nine 

 seedlings the percentage of survival has been much higher 

 than on the area as a whole. These considerations, together 

 with the seasonal fluctuation in death rate, lead me to conclude 

 that the ''vicissitudes" and ''chances'' which determine the 

 survival of Palo \'erde seedlings are almost wholly physical, as 

 distinguished from the so-called biological conditions, which is 

 to say the physical conditions which are initiated by assoc'ated 

 plants. By far the most important of the physical conditions 

 are those which have to do with the maintenance of the trans- 

 piration-absorption balance of the seedlings. 



The Desert Laboratory, 

 Tucson. 



TPIE COMMERCIAL RAISING OF SEEDS 



A. J. PlETERS 



The personal experience of the writer has been confined to 

 the raising of vegetable and sweet pea seed, but the fundamental 

 problems are much the same in all kinds of seed raising, diffeiing 

 more in details than in the nature of the problems. In geneial, 

 these may be grouped under two heads, the growing of the seeds, 

 "making the crop," and the selling of them. The latter is per- 

 haps the most difficult, and the root of probabl} nine-tenths of 

 the trouble of the honest seedsman is to be found in the matter 

 of price. 



