Page:Popular Science Monthly Volume 81.djvu/331

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rived at an economic maximum. It may then be concluded that assuming an even stand of a ton to the acre, it requires 15 acres to supply one ton a year, allowing for good years and bad. Most guayule land will not yield so well. It is, however, clear that where the land is very cheap and can be used for other profit to a considerable extent without materially damaging the shrub, a conservative method of gathering could have been made to yield reasonable and constant returns.

It has been assumed that the stand is maintained by the reproduction of guayule by seed. Field studies have shown that this is true. Areas of known dimensions have been cleared of all plant growth, and the new seedlings counted; and censuses have been taken of such areas to determine the population of plants of various ages. The information obtained proves clearly that the more usual method of reproduction is by seed. It must be added that different localities often not widely separated show a very diverse efficiency in this regard. Indeed, it has often been difficult to see any evidence that if the present growth were removed there would be any effectual replenishment by seed. Such places are marked by the absence of small seedlings and usually carry only mature individuals of approximately the same size. But it by no means follows that in such situations there is no reproduction at all, for in addition to seedlings the guayule also increases its members by means of "retoños," that is, by new shoots which strike upward from the shallow lying lateral roots. In the course of time retoños establish their own roots and become entirely separated from the rest of the plant and consequently independent organisms. Retoños grow more quickly than seedlings and are more certain of arriving at maturity. Because of the previous establishment of the root they may develop where, on account of slight depth of soil, seedlings would fail. As a matter of fact they are relatively more plentiful on rough stony ground and are particularly prone to occur where the surface of the ground is steep and the roots become exposed by erosion, though this is not a condition necessary to their formation. Furthermore, they develop flowers in the first season of their growth so that, in the event that the guayule were removed they would constitute a pretty certain insurance against extinction.

Whether the cutting away of the aerial portion of the plant induces the growth of retoños or not has not been decided, but, as already said, it is followed by abundant reproduction of new shoots from the stocks left in the soil. These follow cutting in about 40 per cent, of the cases, so far as determined, but as the year when the censuses were made was a dry one the figure is probably low for a good season. The time when the cutting takes place doubtless also influences the result. Aside from this, however, these new shoots develop rapidly, but flower abundantly in the first season and are thus effective in reseeding the ground.

We see, therefore, that the guayule is by no means unequipped for