IQ2o] 



B UCHHOLZ—POL YEMBR YON Y 



161 



separate units, the suspensor cells back of the embryo become 

 easily separated from each other. 



Discussion 



It will be seen that among the 7 genera of the Abietineae 

 examined, the last three do not possess cleavage polyembryony 



in 



instances. 



in 



9 



Pinus 



10 



Cedrus 



11 



Tsuga 



12 



Abies 



13 



14 



Picea Larix 



15 



Pseudo- 



tsuga 



Figs. 9-15. — Embryos of 7 genera of Abietineae, showing intergrading series with 

 cleavage polyembryony on the one hand (figs. 9-1 1) and its absence on the other 

 (figs. 12-15); rosette embryos in Pinus, Cedrus, and occasionally Abies; diagrams not 

 drawn to scale. 



and Cedrus, and only rarely in Abies, while none of the other forms 

 shows them even occasionally. Cedrus and Tsuga are most like 

 Pinus in possessing cleavage polyembryony as a constant feature, 

 but in the latter the rosette cells do not produce rosette embryos. 

 Rosette cells, even though they produce no embryos, as in Tsuga, 

 Larix, and Picea, are clearly homologous with these embryo initials 

 in Pinus and Cedrus, and represent vestigial structures wherever 

 they are present. Figs. 9-15 illustrate these differences. We have 



* 



