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Polyembryony in Nn^ Bearing Pines 297 



POLYEMBRYONY IN CERTAIN NUT BEARING PINES. 



D. M. MOTTIER, Indiana University. 



In seeds of nut bearing pines, "pinyon nuts", used for class study, 

 the presence of two embryos in individual seeds has been observed from 

 time to time. During- the autumn of 1922, a member of the class called 

 my attention to two well developed embryos of nearly the same size in 

 a seed, probably of Pinus ednlis Englemann, given him for study. Closer 

 examination revealed the fact that in this seed three other smaller em- 

 bryos were also present, making five in all, as shown in figure 1. The 

 three smaller embryos are large enough to be recognized by the un- 

 aided eye. The figure represents the five embryos in proper proportion. 

 In the three smaller embryos no indication of cotyledons could be rec- 

 ognized with the hand lens. The two larger embryos seemed to be ma- 

 ture as regards the differentiation of parts. The one near the chalazal 

 end is perceptibly larger. In cases in which only one embryo is present 



Fig. 1. Onc'-hair of endosperm of Finns edulus, showing: the five embryos in 

 position. X 6. 



in the mature seed, the length of the embryo is almost equal to the 

 length of the endosperm. 



As is well known, polyembryony in the genus Pinus results from 

 the cleavage of the pro-embryo into four embryos, all of which tend 

 to develop, but owing to competition, embryonal selection results, and 

 only one embryo, as a rule, matures in the seed. If only one egg be 

 fecundated, we have mono- zygotic cleavage polyembryony. But if two or 

 more eggs are fecundated, as frequently happens in some species of 

 pines (P. laricio) , we have what may be termed poly-zygotic cleavage 

 polyembryony. In Gymnosperms in which the embryonal cells do not 

 separate, and one embryo develops from each fecundated egg, poly- 

 embryony can result only from two or more fecundated eggs. This is 

 simple poly-zygotic polyembryony. 



In cases of poly-zygotic cleavage polyembryony in Gymnosperms, 

 it is very evident that among the numerous embryos that begin develop- 

 ment, with apparently an equal start, the struggle for supremacy is 

 very intense. The instance of figure 1 shows that the two larger were 

 almost potentially equal, the one being unable to crov/d out the other. 

 Each, however, is about one-half the size of the single embryo normally 



"Proc. 38th Meeting, 1922 (1923)." 



