LIFE HISTORY OF PINUS 



but he does note a most interesting transfer of nuclear sub- 

 stance, that is, a substance secreted by the nuclei, from the 

 nuclei of the sheath-cells into the cytoplasm of the egg. In 

 the course of his discussion Ikeno says : " Bemerkenswerth ist 

 es ferner, dass der Zellkern der Wandungszelle haufig sich der 

 Centralzelle nahert und dort einen nach dem nachsten Plasma- 

 faden gerichteten kurzen Schnabel bildet (fig. 6). In einen 

 andern Fall beobachtete ich, das der Zellkern der Wandungs- 

 zelle sich bis an die Cellulosemembran begiebt, welche an die 

 Centralzelle angrerizt und mit dem ganzen Korper an diese sich 

 anlegt (fig. 7, #, b). Offenbar sollen alle diese Vorgange den 

 Uebergang des in diesen Zellkernen enthaltenen Stoffes nach 

 der Centralzelle erleichtern." So far as I am aware then, 

 Arnoldi is the only investigator who has observed the passage 

 of entire nuclei into the egg in the Gymnosperms. 



Some interesting observations have been made during this 

 study regarding the nature of the nucleolus of the egg-nucleus. 

 As already indicated this nucleolus does not arise in Pinus 

 Strobus until the egg-nucleus has attained considerable size. 

 It appears in the lower part of the nucleus as a minute, solid, 

 spherical body ; during growth a small central vacuole appears, 

 then other vacuoles, until, at maturity, it is completely filled 

 with vacuoles of various sizes (figs. 202-205, plate XVIII). 

 A limiting membrane is not always apparent in this nucleolus 

 (fig. 208, plate XIX; but in some instances, there seems to be 

 very strong evidence of such a membrane (figs. 205 and 209). 

 In fig. 205 the nucleolar wall has been broken at one place 

 and a vacuole, lying near the point of rupture, has been in- 

 dented along its outer surface, thus becoming crescent shaped. 

 Montgomery ('98) sounded a word of warning against inter- 

 preting the peripheral stratum of the ground substance of the 

 nucleolus as a wall layer; and there is a possibility that, in the 

 figures above referred to, what appears like a limiting mem- 

 brane is only the outer unmodified portion of the nucleolus. 



The attitude of this nucleolus toward dyes varies much at 

 different periods in its history. It may or may not take the 

 safranin stain characteristic of Flemming's triple combination ; 

 it may stain intensely with gentian-violet or iron haematoxylin 



Proc. Wash. Acad. Sci., August, 1904. 



