1920] BUCHHOLZ— POLYEMBRYONY 165 



larix. The later embryo and other anatomical features of Keteleeria 

 are described by Hutchinson (8) , but the early embryo still remains 

 to be studied. Pseudolarix was described by Miyake and 

 Yasui (16), whose work shows stages in the embryo similar to 

 tigs. 2, 4, and 6, with a figure showing the suspensor cells beginning 

 to elongate. This species has rosette cells and appears more 

 slender, but is otherwise like the average of the Abietineae in 

 the same stage of development before the embryo units separate 

 (if they do). This embryo is not like Pseudotsuga, therefore, but 

 probably belongs somewhere in the series (figs. 9-15) between 

 Tsuga and Picea, the exact position depending upon whether or 

 not cleavage polyembryony occurs, and whether the rosette cells 

 give rise to rosette embryos. 



Some taxonomists include Pseudotsuga in the same genus with 

 Tsuga. The results of this investigation show that, on the basis of 

 the embryogeny at least, there is a fundamental difference between 

 these two forms, which would entitle Pseudotsuga to be recognized 

 as a separate genus. The contrasting differences may be sum- 

 marized as follows. Tsuga has cleavage polyembryony and api- 

 cal cell growth in its life history, while Pseudotsuga has none of 

 these features ; and while the rosette cells do not produce embryos 

 in Tsuga, they are either entirely absent in Pseudotsuga or they 

 elongate to form the suspensor and are not recognizable. The 

 latter genus has also 5-8 archegonia, while Tsuga usually has a 

 smaller number (2-4). 



It should be noted that the difference between the embryo 

 of Pseudotsuga and Tsuga is greater than that between Abies, 

 Larix, and Picea, and much greater than that between Pinus and 

 Cedrus. Cedrus, on the other hand, shows little in its early embry- 

 ogeny which would entitle it to a place as a separate genus, but the 

 difference between Pinus and Cedrus is nearly as great as that 

 between Larix and Picea. 



Summary 



1. Although all species of Pinus have shown a complete 

 separation of the 4 primary embryos, this feature of cleavage 

 polyembryony is not characteristic of all Abietineae. 



