LIFE HISTORY OF PINUS 6l 



centrosome in the cells of the higher plants was suggested by 

 Guignard in 1897 and was again hinted at by Le Dantec in 

 1899. If we may accept Guignard's suggestion, then the kinetic 

 center of the cell in the higher plants is no longer indicated by 

 the presence of a definite organ, the centrosome, but the power 

 of this organ has become dissipated throughout the entire cell. 

 When that phase of cell-activity which has to do with spindle- 

 formation comes into play, the points at which it is centered 

 would naturally be indicated by a greater accumulation of the 

 microsomes, and thus an aster of more or less definiteness would 

 be formed, as when the individualized centrosome is present. 

 In the division of the generative nucleus in JPinus, the position 

 of the nucleus is such that the energy active in spindle-forma- 

 tion must perforce, if external to the nucleus, be centered at 

 some point below it. Such a centering of the activity would 

 naturally result in an attraction-sphere of unusual prominence ; 

 and there would be no occasion for its division since there is not 

 sufficient space above the nucleus for the organization of kino- 

 plasmic threads. 



When these studies were undertaken, it was thought that it 

 would be interesting to determine whether any suggestions or 

 remnants of a cilia-forming body (called blepharoplast by Webber 

 in Zamid) still persist in the Conifers. Somewhat later, after 

 the present research was begun, MacMillan ('98) pointed out 

 the desirability of such a study both in Coniferce and Gnetales. 

 I have seen no indication of a structure which might be regarded 

 as a reduced blepharoplast, or as suggestive of a cilia-forming 

 body of any sort in connection with the formation of the sperm- 

 nuclei in Ptnus. Inasmuch as spermatozoids do not exist here, 

 such an organ, if present, must be functionless. But the cyto- 

 plasmic radiations which accompany the division of the genera- 

 tive nucleus in its early stages seem to differ in degree only from 

 those found by Webber ('97) in the generative cell of Zamia. 

 If we compare figs. 3 and 5 of Webber's paper with figs. 96 and 

 97, plate IX, of this paper, the question may be raised whether 

 in this cytoplasmic figure we may not have still persisting in 

 the cell the last vestiges of such an organ as that described by 

 Webber. 



