68 Guayule. 



her but smaller than those left when the shrub is cut. The larger break 

 off further in the ground and are therefore less favorably placed for starting 

 afresh. The disadvantage of the cutting method in the eyes of those who 

 are in pursuit of the greatest possible initial return is that less tonnage 

 per acre is obtained, a loss, however, which would be made good many 

 times in new plants if the roots were properly cut and allowed to remain. 



SEED. 



VIABILITY. 



The seeds of guayule appear to have a fairly long period of vitality , 

 a conclusion, however, which is inferential and has not been demonstrated 

 by direct experiment. The view is based on the following experiment 

 (exp. 78): On November 23, 1907, a lot of trays (such as are shown in 

 plate 45) were filled with paper tubes of i square inch transverse section. 

 The trays were then filled with soil made up of half and half garden soil 

 and old dry manure from a horse corral. In the top of each tube were 

 sown 20 to 30 seeds. The trays were watered abundantly by subirriga- 

 tion, it being the purpose to try the method of using the trays with paper 

 tubes for wholesale germination. So far as this was concerned, the experi- 

 ment was a failure, but it served to contribute to our knowledge of seed 

 vitality. The very dry season made it very difficult to keep the surface 

 soil moist, and as a result of alternate drying and wetting the upper part 

 of the soil became caked and there was considerable efflorescence of salts. 

 The soil below became soggy and sour, and fungi permeated the soil and 

 the paper of the tubes. Very few seeds germinated, not more than one 

 or two in each tray, partly, as was later determined, because of the char- 

 acter of the soil, and partly because of the prevailing low temperatures. 

 The trays lay thus, occasionally wet by showers, till the following July, 

 when a large number of seeds started to germinate. In one tray 138 tubes 

 had seedlings, from one to eight in each. By July 25 the seedlings had 

 developed two foliage leaves, and by August 28 a stem-growth of 5 cm. 

 was not exceptional, with leaves 5 cm. long. Some plants had at this 

 date as many as seven foliage leaves. Thus it will be seen that the seeds 

 which germinated did so after six months' exposure to conditions about 

 as bad as could be imagined, being alternately wet and dry, in a sour 

 soil, and open to the attacks of fungi. The germination in trays favorably 

 placed with respect to shade was upwards of 13 per cent of viable seed, 

 as nearly as may be calculated. 1 It may therefore be concluded that the 

 seed of guayule, being neither very short-lived nor very sensitive to unto- 

 ward conditions, is, from a biological point of view, quite efficient for the 

 preservation of the species. 2 



It is, in the nature of the case, well-nigh impossible to determine 

 the percentage of germination of nature-strewn seed, but one successful 

 experiment affords us exact data (experiment 192). On May 30, after a 



1 Critical germination tests to determine the viability of seed have been 

 made by Kirkwood (19100), who finds the germinations to scarcely exceed 14 per cent, 

 and that after eight months there is a marked drop in viability. 



2 Ready germination front* seed collected during the summer of 1908 was 

 obtained in July 1909, at Auburn, Ala. 



