CHAPTER IV. 

 REPRODUCTION. 



METHODS OF REPRODUCTION. 



It is the purpose of the present chapter to compare the two methods 

 of reproduction, sexual and vegetative, with reference to final efficiency 

 in reproducing the species. It need scarcely be said that, in speaking of 

 sexual reproduction, we are using the term to indicate the origin of the 

 seed. It will be at once accepted that accurate knowledge of the topic here 

 to be considered is of vital importance in deriving estimates of the rate 

 at which guayule fields may be expected to produce a crop of that plant. 



From what has been said in the foregoing chapter it will be seen 

 that, taking different kinds of habitats into account, an average rate of 

 reproduction will be maintained by means of the retofio and seed methods 

 combined. The relative efficiency of the two methods depends upon 

 widely different considerations, and these, as we shall now see, have rela- 

 tion to numbers of individuals, rate of growth, and the time of the year at 

 which they begin this growth. 



RETONOS, NORMAL AND INDUCED. 



We may speak of two kinds of retonos, normal and induced. By 

 normal we mean those which arise spontaneously upon the lateral, 

 superficially placed, horizontal roots, remaining for some time attached 

 to the plants from which they spring (plate 9). Induced retonos (plate 

 15) will then be those which arise as the result of mutilation, that is, 

 from roots, primary or of a higher order, after the plant has been cut 

 away. This is done on a number of haciendas in the harvesting of the 

 shrub, whereas the plants used to be, and by many still are, pulled up by 

 the roots. This pulling results, of course, in breaking away many of the 

 roots, but the chief portion of the tap-root is removed, as also are consid- 

 erable lengths of the other roots. As we shall see, the difference in effect 

 upon reproduction is merely quantitative, as in both cases retonos may 

 arise, but in very different numbers. In order to test this with as great 

 accuracy as possible, quadrats of 100 square meters were cleared of the 

 guayule both by the cutting and pulling methods, and the results were 

 noted. These, for the quadrats observed, afford accurate data, which 

 must be understood as of indicatory value only. It may well be believed 

 that different meteorological conditions would have modified the results 

 very considerably. Thus, if the experiments had been started just at 

 the beginning of the summer rainy season more hopeful results might 

 have been had, but we shall see that cutting at this time is for other 

 reasons an unfortunate practice, and the evil resulting would offset the 

 value of the data thus obtained. It is well, therefore, for economic rea- 

 sons, that the data collated shall be well within bounds. In addition 

 to experimentally obtained data, others derived from observation are 

 given, and have already been discussed in part in Chapter III. 



61 



