i 9 2o] BUCHHOLZ— POLYEMBRYONY 159 



There are from two to four archegonia present in Tsuga, and in 

 the material studied one or two embryo systems was the usual 

 number found. The cones were very poorly pollinated, and 

 doubtless the normal maximum number did not occur. Poly- 

 embryony, although extensive, is much less pronounced than in 

 Pimis, for in addition to the small number of archegonia, there are 

 no functioning ros.ette embryos. 



In Abies the normal product of a fertilized egg is a single embryo. 

 The group of rosette cells is present, and in a few rare instances a 

 divided rosette cell and a more advanced rosette embryo were 

 found. This, as well as the fact that cleavage polyembryony was 

 also observed in a few cases, shows that this genus stands next to 

 Cedrus and Tsuga in its similarity to Pinus. 



The apical cell stage is doubtless eliminated from the beginning, 

 for when under normal conditions all of the lower tier of cells com- 

 bine to produce a single embryo, the terminal cells together are 

 responsible for producing the tissue. It appears also from an 

 examination of some of the early embryos that these 4 terminal 

 cells of the apical group do not always contribute equally to the 

 cell mass, for one of these 4 terminal cells may frequently be found 

 decidedly more prolific than the others. Normal apical cell growth, 

 however, is not possible unless cleavage polyembryony occurs, 

 as it rarely does. 



The suspensor cells and upper embryonal tubes of the secondary 

 suspensor collapse very soon after elongation. The basal plate 

 (bp), a deposit formed within the egg over the rosette cells, is very 

 thick and frequently obstructs a clear view of the rosette cells, 

 which also collapse early, unless a rosette embryo happens to 

 develop. 



The material of Picea was somewhat limited. The cones that 

 could be secured of P. mariana were younger than the fertilization 

 stage, and a later collection was too old for a satisfactory study of 

 the early embryo. A number of twigs bearing cones from the 

 first collection were kept in a tin box in the laboratory for more than 

 a week, and at the end of this time they were found to contain 

 embryos in the desirable stages. The P. excelsa cones were very 

 poorly pollinated, and only a few good embryos were secured from 



