Renewal of Growth by Guayule Transplants.

Guayule seedlinos were received fromi the federal nursery of the Emergency Guayule Project at various times of the year for use in a general study of the growth of this species under greenhouse conditions (1). Stock removed from the nursery at different times of the year showed markedly different powers of regenerationi when transplanted to soil in the greenhouse. The best growth was obtained from stock transplanted from the nursery during the winter. As the season advanced fromii winter toward summer, a progressive decrease was observed in the ability of nursery stock to resume Trowth in certain soils. The resumption of growth of stock received from the nursery in June was very poor. A comparison of regeneration in soil eontrasted with that in water culture is of particular interest. Seedlings were shoot pruned in the nursery beds at successive intervals from late December, 1942, to early July, 1943. Shortly thereafter, as is usual in preparing for transplantation, these seedlings were removed from the soil after partial root pruning. The effects of pruning were accentuated at the time of experimentation by further abscission to reduce the transpiration surface to a minimum and by root trimming to expose fresh root surfaces for more ready entry of water. Seedlings were transplanted as soon as convenienit after shipment-usually 1 to 2 weeks after removal from the nursery soils. Whenever possible, storage temperatures were maintained at about 15° C. Experimeents were performeld in vessels containing nuLtrient or soil media. Successive lots of planits tranisplanited into the samne type of soil renewed growth progressively miiore slowly, anid the perceentacre regeneration decreased. The same phenomenon obtained when plants were placed directly in nutrient solutions-however, to a much smaller degree. In aqueous solutions the regeneration at all times was miiore rapid and a larger percentage of renewed growth was obtained. Withini relatively wide time limits the absolute regeneration observable is merely a measure of rate. The rate of renewal of growth is possibly related, in one way or another, to the time of shoot and root pruningy in relation to the phase of the plant's periodic growth cycle. Conceivably, the availabilitv of moisture in soils is a prime factor governing the regeneration relative to nutrienit solution cultures. To test this point, wheni resumption of growth in soils was otherwise poor, successivelv iniereasing average miioisture pereentages were mnaintained in lots of Fresno fine sandy loam and Danville clay loam (fromn Richmond). The rate of