156 BOTANICAL GAZETTE [February 



its competitors. Embryonic vigor in producing a long suspensor is 

 the outstanding factor which decides upon the successful embryo. 

 The mass of embryonal tubes which elongate from the base of the 

 embryo, as this and the suspensor become more massive, doubtless 

 assist the successful embryo in checking the others. Usually it is 

 the embryo foremost in position which is successful in developing 

 to maturity, but sometimes the second one in position becomes 

 massive more rapidly and assumes the leading role, by choking out 

 the smaller terminal one. Not only must an embryo have a rapidly 

 developing suspensor, but it must also become many-celled and 

 massive more quickly than any of the competing embryos. 



Vigorous suspensors have been the basis of selection among the 

 embryos of gymnosperms for so long a period that this organ has 

 become a large and extensively developed structure, many times 

 larger than would be necessary without this embryonic competition. 

 This is true whether the competing embryos come from the same 

 egg, as in cleavage polyembryony, or the selection occurs between 

 neighboring zygotes, as among cycads. The remarkably long 

 suspensor found in nearly all gymnosperms has always been a note- 

 worthy feature of this group. 



Investigation 



Other pine species. — The result of a further investigation of 

 the embryo development in various species of pines confirmed the 

 account as announced for Pinus (3). The additional work done 

 on Pinus Strobus, P. ponderosa, P. edulc, and P. rcsinosa, as well as 

 a further examination of P. Laricio, P. Banksiana, and P. sylvestris, 

 makes it practically certain that cleavage polyembryony, the apical 

 cell development, and the rosette embryos are found quite con- 

 stantly among all members of this genus. 



It might be noted that Pinus sylvestris seems to have a marked 

 tendency to produce shorter suspensor cells and embryonal tubes 

 than P. Banksiana, which was taken as the type for the previous 

 investigation. In P. Laricio the 4 primary embryo units frequently 

 do not split apart until the primary suspensor cells have stretched 

 to about half their final length and the first embryonal tubes are 

 beginning to elongate. Indeed, when some of these earlier stages 



