Further studies on polyembryony and germination of polyembryonic pine seeds.

THE OCCURRENCE of two well developed seedlings from the same seed is very rare among pines. Toumev (1923) reported one instance of two well developed and normal seedlings from one seed of Pinus thunbergii Parl., and Jacobs (1924) found while investigating the germination of seeds of Pinus lambertiana Dougl. (Sugar Pine) that one per cent developed two seedlings each. The development of such "twin" seedlings from the same seed is no doubt the result of two equally, or nearly equally, developed embryos. It is well known that several embryos, four or more, are always present in the pine seed during the early stages of development; usually only one survives at maturity of the seed. The persistence, therefore, of more than one embryo to maturity and even to the stage of germination presents a feature of considerable interest. Such embryos can be demonstrated by the dissection of pine seeds. Germination tests and dissection2 of the embryos from mature seeds comprise the two methods used in this study. POLYEMBRYO NY.-Polyembryony is the formation of two or more embryos within the same seed coat. Sometimes these embryos are so arranged and developed that they have the ability to germinate and produce two individual seedlings. Germination tests of the large seeded pines, with special attention to the occurrence of multiple seedlings, has yielded a number of instances of two well developed seedlings from the same seed, according to Clare and Johnstone (1931). 1 Received for publication July 2, 1940. 2 Acknowledgment is hereby accorded Miss Dorothy F. Ellinwood of Jokake, Arizona, for data on dissection of pine seeds and Miss Elisabeth Moskedal of Downey, California, for data on germination. The most intensive investigations of the morphology of polyembryonic seeds are those of Buchholz (1926, 1929), which present in detail the morphology of the developing embryos, the struggle for survival among the young embryos, the final condition of the mature seed, the two forms of polyembryony, and the occurrence of cleavage polyembryony which must have been the primitive condition through which all conifers have passed. His work, though intensive, does not deal with germination. The actual germination of polyembryonic coniferous seeds has been observed by Toumey (1923), Jacobs (1924), Clare and Johnstone (1931) and others. Toumey states his inability to find records of previous investigations on the subject. One of the more recent and extensive investigations is that of Clare and Johnstone (1931) who review the literature on the subject to date, and report from their investigations the occurrence of six instances of multiple seedlings, two having been found in each of three species: viz., Pinus torreyana, P. sabiniana and P. cembroides var. monophylla. The literature on the embryology of the Gymnosperms has been reviewed bv Schnarf (1933), who states that polyembryony in the sense of the occurrence of several embryos within the same seed is very frequent among the Gymnosperms, while the appearance of more than one living, healthy seedling originating by germination, forms an exceptional case. More attention to this phenomenon, however, may reveal multiple seedlings among a larger number of species. It is the present purpose to give a full account of data on the occurrence of multiple seedlings from seeds of pine, heretofore published in part as a preliminary announcement, Johnstone (1936).