84 



Guayule. 



Table 37 gives measurements for the years indicated of 3 " spindling " 

 plants, which grew rapidly in height but did not develop branches and 

 therefore weight. 



Plant 7 was 50 cm. tall and weighed 153 grams, ragged, but showing 

 abnormal development on certain shoots. The last three years of its 

 growth showed accretions, a side-shoot starting low down, of no, 200, 

 and 60 mm. The upper shoots appeared quite similar to those of the 

 other plants, but were more or less damaged, so that one could not get 

 satisfactory measurements. 



The conclusion one is forced to draw from a survey of the above 

 tables is that in a certain proportion of the plants in the locality referred 

 to the rate of growth per year approaches closely to 50 mm. In these 

 plants, however, the branches are thin, and the plants are not well devel- 

 oped nor heavy for their size, so that, economically considered, there is 

 nothing gained. Whether the differences in rate of growth are connected 

 with racial differences in the plants is discussed elsewhere. 



RATE OF GROWTH IN IRRIGATED PLANTS. 



A considerable number of plants were under observation for the 

 whole of two growing-periods, during which time they were freely irri- 

 gated ' and grew rapidly, at a rate close to the rhythmic maximum. The 

 average rate of growth for the two years was very close to 25 cm. per 

 year, so that a spread of a meter was attained by nearly all of the plants. 

 The character of the growth is described elsewhere, but the fact here 

 stated indicates very clearly that plants in the field may never be ex- 

 pected to reach this maximum. The greatest growth of stem-length in 

 field plants for one year, 200 mm., was seen in a very few twigs and in 

 shoots favorably placed, the rest of the plant failing to behave similarly. 



The weight attained in two seasons by irrigated plants growing 

 from small butts after transplanting is upwards of 2 pounds, or slightly 

 over. The fresh weight of a large plant was 4.5 pounds. Another col- 

 lected at the same time weighed fresh 3.5 pounds, and shrank in drying 

 to 1 pound 10 ounces. The dry weight of two others was 28 and 32 ounces. 



On the other hand, plants under limited irrigation were grown at 

 Caopas. I have examined three sample individuals of these, a large, a 

 medium-sized, and a small plant. All of these failed to start promptly, 

 and had been pollarded. The amount of growth made by them is shown 

 in table 38. 



Table 38. 



1 In 1907, through the winter until the following April. They were not irri- 

 gated later, but received rain in the summer. They had a sufficient amount of 

 soil-moisture for continuous growth. 



