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SCIENCE 



[N. S. Vol. XXXIV. No. 885 



the native soil of the Guayule than in the al- 

 luvium of the garden, where the experimental 

 grounds were located, which resembles the soil 

 of the playa. It would, moreover, seem un- 

 likely that acidity exists in this soil in the 

 presence of carbonates. At all events the 

 greater concentration of the salt solutions in 

 the soils of the lower plain, as a possible addi- 

 tional factor affecting the distribution of 

 Guayule, is well worth consideration. This 

 conclusion is supported by the fact that the 

 alluvial soil proved inimical to the growth of 

 seedlings, a fact which Professor Lloyd else- 

 where recognizes, and that this was not due 

 to mechanical conditions alone has been dem- 

 onstrated in carefully conducted experiments.' 

 Some of the alluvial soil used was fatal to the 

 Guayule seedlings at first, but after leaching 

 offered no obstacle to their development (page 

 68), additional evidence that the salt content 

 is in this case an important factor. 



Discussing the subject of the size and form 

 of the Guayule plant, the author states the 

 upper limit of weight to be about 5 kilos and 

 of height to be about one meter. The mature 

 plants are profusely branched, the leaves and 

 younger twigs being clothed with a silvery 

 pubescence. The root-system, distributed 

 chiefly through the superficial layers of the 

 soil, is partly concerned with the usual work 

 of absorption and partly with the function of 

 vegetative reproduction, accomplished by 

 long, slender members from which arise shoots 

 called retonos. The identification of two bio- 

 types is a matter of special interest. As to 

 whether there were two distinct forms of the 

 Guayule was a subject frequently discussed at 

 Cedros. Observers sometimes remarked two 

 forms of the plant, yet when an effort was 

 made to delimit the characters of the two 

 forms definitely, their distinctive marks 

 seemed quite elusive. It would seem that the 

 author of the present paper has happily dis- 

 covered the line of cleavage. 



Under the topic of reproduction the func- 

 tion and importance of the retofio is discussed 

 at length. As a means of reproducing a 

 stand of Guayule the retoiio is not found to 

 be very effective. Eegeneration of the stand 



is brought about much more rapidly by cut- 

 ting off the shrub instead of pulling it up in 

 the harvesting process. Eeproduction by seed 

 is slow and only takes place at all on open 

 ground under the most favorable conditions. 

 The author concludes that a ten to fifteen 

 year rotation is practically possible and eco- 

 nomically advantageous, the average rate of 

 height growth being about 3 cm. per annum. 



The chapters on the anatomy of the plant 

 (V. and VI.) present a detailed description of 

 the structure of the young and mature plants 

 in root, stem and leaf. In this connection it 

 is interesting to note the effect of irrigation 

 on the relative development of wood and bark. 

 The volume ratio of bark to wood in the irri- 

 gated plant is near to unity in the smaller 

 twigs to 0.27 in the larger, up to 13 mm. in 

 diameter. In field plants the ratio for the 

 smaller twigs approaches 2.5, being reduced 

 to 1.7 for stems 13 mm. in diameter and ap- 

 proaching unity in those larger. On the other 

 hand, in point of age the ratio of total bark 

 produced in the irrigated plant to that of the 

 field plant of the same age is about 5.6. 



On the origin and occurrence of rubber 

 (chapter VII.) the author informs us that 

 9.5 per cent, of the dry weight of the shrub 

 is rubber. This is distributed through the 

 pith, medullary rays and inner bark. The 

 quantity of the rubber secreted and the time 

 of secretion stands in relation to the water 

 available and the seasonal activity of growth. 

 Very little rubber is secreted during the period 

 of active growth, and relatively little at any 

 time in irrigated plants, but secretion proceeds 

 more rapidly with the advance of the dry 

 season. The function of the rubber in the 

 economy of the plant seems obscure. 



The concluding chapters deal with the ex- 

 perimental operation on vegetative reproduc- 

 tion, with seeding, and with proposed methods 

 of cultivation. The author takes a hopeful 

 view of the possibilities, and believes the solu- 

 tion of the problem of successful propagation 

 not to be beyond the limits of practicability. 

 From the evidence adduced it would seem that 

 this may be possible, but the evidence also 

 seems to point to the conclusion that an ade- 



