LIFE HISTORY OF PINUS IO7 



At about the time of the cutting off of the ventral canal-cell 

 man}' small nucleolus-like masses appear in the nuclei of the 

 sheath-cells — twenty or more occurring in a single nucleus. 

 When the egg has reached maturity, and during the later stages 

 of its histor}', no nucleolus, or but one or two nucleoli, can be 

 demonstrated in the nucleus of a sheath-cell. These nucleoli 

 are no longer surrounded by a hyaline court, but are imbedded 

 in the chromatic network. 



The nucleoli of the sheath-cells present the same attitude 

 toward stains as does the nucleolus of the egg-nucleus. But 

 ■while the nucleoli of the sheath-shells frequently stain but feebly 

 they rarely fail entirely to stain. 



Similar color reactions have been observed in connection with 

 the nucleoli, as already described, in the microspore-mother cell 

 of Pinus. The occurrence of unstained nucleoli in the same 

 nucleus in which others were deeply colored is common in the 

 microspore-mother-cells especially at about the time of synapsis. 

 I am aware that conclusions based upon staining reactions alone 

 are not to be trusted, but when accompanied, as here, with other 

 phenomena they may be highly significant. 



The nucleolus of the egg-nucleus and also the nucleoli of 

 the sheath -cells in Pinus appear to represent active portions of 

 the cell rather than inert masses of matter. Certain aspects 

 presented by these nucleoli are surely suggestive of plastids. 

 The uncolored framework of the egg-nucleolus reminds one 

 very strongly of a chlorophyll body from which the pigment 

 has been extracted. Yet we would not, in the present state of 

 our knowledge, denominate them plastids. I believe, however, 

 although the phenomena are not of such a nature as to admit of 

 definite demonstration, that the nucleolus of the egg-nucleus, 

 and also the nucleoli of the sheath-cells are actively engaged in 

 the formation of a substance which in the egg-nucleus, at least, 

 assumes the shape of secondar}^ nucleoli. These nucleoli be- 

 come diffused throughout the nucleus, from which they pass, 

 probably in solution, into the egg cytoplasm. Here they are 

 again differentiated, and by a gradual development, give rise 

 to the " proteid vacuoles " or nutritive spheres of the oosphere. 

 It may be that the greater size of the egg-nucleus, in com- 



