54 EMBRYOGEXY OF Pinus Pinastcv. 



•ceil, and the writer is inclined to believe that the apical cell is still 

 functional up to about the age of the embryo of figure lo, i.e., 

 about a 30-celled embryo 



Figure 4 shows a peculiarity which the writer is unable to explain, 

 namely, two suspensors supporting an embryo with but a single 

 apical cell. Usually, as stated above, there is an apical cell corres- 

 ponding to each suspensor cell, i.e., where two suspensors remain 

 associated, two apical cells are functional, derived respectively 

 from the two original embryonic cells, or where all four suspensors 

 remain connected there will be four apical cells. Whatever the 

 explanation of figure 4 may be the series from which the drawing 

 is made cannot be interpreted in any other way than as shown in 

 the figure. In no case is another apical cell to be found in other 

 sections of the series. The top embryo in figure 8 looks at first 

 sight like another case of the same kind, but the two proximal cells 

 here are young embryonal tubes, not the distal ends of suspensors. 

 ■Campbell (2) figures and describes a similar case in Pinus insignis 

 ■{see his figure 306 c). After a time the apical cell or cells become 

 replaced by a groupof initial cells as mentioned by Campbell (ioc.cit.) 

 Figure 7 represents an example of two embryos remaining closely 

 associated, but developing independently, a state of things which 

 reaches its climax in the somewhat rare phenomenon of incomplete 

 twin formation. Attention is directed to this figure, since an ex- 

 ample of the phenomenon referred to has recently been described 

 and figured in Widdringtonia [Morris (13)], apparently the first re- 

 cord of its occurrence in a Gymnosperm. 



The next stage figured (figure 12), an embryo of approximately 

 2,000 cells,* shows an interesting feature. Karyokinetic activity 

 has now been almost entirely transferred to the proximal end of 

 the embryo, and has resulted there in the formation of the periblem. 

 The early appearance of the root meristem in Gymnosperm em- 

 bryogeny was first pointed out apparently by Lyon (12) for Ginkgo, 

 and has been recently described by the writer ( 15) for Encephalartos. 

 It is to be noted however that the phenomena now described in 

 Pinus are absolutely different from those which occur in Ginkgo 

 and Cycads. In the latter the first differentiation is between root 

 and stem, whereas in Conifers (probably this is a safe generalisation) 

 it is between the perihlem and what later forms the remaining 

 morphological regions. 



The writer believes that this has not previously been pointed 

 out, although various investigators have published figures of 

 Pinus from which the fact might have been deduced. 



A figure of an embryo of Podocarpus is given in Coker's (3) 

 account of this genus very similar to the one here given for Pinus. 

 Of this embryo (figure 49 loc. cit.) he remarks — 



" There is no indication as yet as to ■v^^here the root-tip is to appear and a 

 distinction between dermatogen, periblem and plerome has not arisen." 



but the shape and arrangement of the cells of the proximal meri- 

 stem indicate distinctly that this is the periblem, while the distal 

 meristem which is fairly sharply differentiated from it, is that which 



* Calculated roughlv from the formula I w r. 



