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BU( HHOLZ— POLY EM BRYONY 



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cell segments (s), the primary suspensor cells, are cut off. This 

 group constitutes what has generally been recognized as the sus- 

 pensor tier of the 16-celled stage (cf. figs. 5, 6). Next the sus- 

 pensor cells (s) elongate and thrust the embryonal tier of apical 

 cells into the pocket which the digestive enzymes of the eggs and 

 embryos have corroded within the 

 gametophyte, the 4 embryo units 

 separating and their apical cells 

 (a) continuing to give rise to segments 

 (e ly e 2 , etc.), which elongate and add 

 to the suspensor. 



Soon the rosette group of initials 

 divides and the development of the 

 rosette embryos is begun (q, fig. 8). It 

 will be seen, therefore, that not only 

 do these 8 embryos per zygote all 

 result from free nuclear cleavages, but 

 the several embryos develop inde- 

 pendently from the time the first walls 

 are organized. The primary embryos 

 develop without interruption from 

 their initials, while the rosette em- 

 bryos are delayed, developing some- 

 what later, on an average, than is 

 indicated in fig. 8. In the hundreds 

 of instances that have been examined 

 in my investigations of various pines, 

 none were found where the 4 primary 

 embryos were combined to produce a 

 single embryo, nor were any cases 

 found where one of the primary em- 

 bryos was further split up to give rise to 2 or more embryos. 



In the competition which ensues, the rosette embryos play a 

 very subordinate role, owing to their unfavorable position and 

 delayed development. Among the 4 primary embryos, the competi- 

 tive process elects one embryo from the complex, nearly always the 

 embryo which develops the longest suspensor, pushing it ahead of 



Figs. 6-8. — Stages in develop- 

 ment of early embryo in Pinus: 

 a, apical cells; s, primary suspen- 

 sor cells; r, rosette cells, which 

 give rise to q, rosette embryos 

 (latter usually develop later than 

 in stage of embryo shown); e x , e 2 , 

 etc., embryonal tube initial cells 

 and embryonal tubes, which elon- 

 gate and add to suspensor; dia- 

 grammatic reconstructions. 



