LIFE HISTORY OF PINUS IO9 



Flemming ('82), Zacharias ('85) and Zimmerman ('93) ascribe 

 to the' nucleolus the dignity of a nuclear organ; and Mont- 

 gomery ('98) makes the following suggestion: "That though 

 the nucleolus consists of substances which stand in some rela- 

 tion to the nutritive processes of the nucleus, and so, at the 

 time of its formation, may be a functionless inert mass of 

 matter, yet it may at later periods in the history of the resting 

 nucleus, acquire some active function, and thus gradually come 

 to acquire the value of a nuclear organ." ^ 



Obst ('99) remarks that the significance of the nucleolus is 

 truly dark, but he considers it to be in some way the result of 

 chemical action whose cause must be sought in the physiolog- 

 ical processes of the cell. A glance at the theories regarding 

 the nature of the nucleolus as briefly outlined above is certainly 

 sufficient to confirm Obst's conviction that our knowledge of 

 the origin and function of the nucleolus is still very imperfect. 

 Yet it cannot be doubted that we have in the nucleolus not 

 merely a mechanical store-house, but a structure which is inti- 

 mately connected with the vital activities of the cell. We still 

 have in the nucleolus a most attractive field for investigation, 

 and the best cytological, physiological, and microchemical 

 technique must be brought to bear upon the problem before 

 we can hope to understand aright the true nature of this 

 structure. 



The Rece-ptive Vacuole. — Immediately preceeding fertiliza- 

 tion a cavity appears in the egg-C3^toplasm, just beneath, or in 

 the near vicinity of, the neck-cells (figs. 211, 213, 214, plate 

 XIX). In some cases this opening may not arise until the instant 

 of fertilization. This cavity, which was thought by the earlier 

 writers to represent the lower portion of the pollen-tube within 

 the oosphere, has been explained by Blackman ('98) as due to 

 the sudden inrush of the contents of the pollen-tube, and by 

 Arnold! ('00) in Cephalotaxtis^ as caused by the downward 

 movement of the conjugation-nucleus. Shaw ('98) suggests 

 that the concavity in the upper part of the egg in Onoclea, just 

 prior to fertilization, may correspond to the receptive spot ; and 

 there is every evidence that in Pinits this opening in the cyto- 



' See note at close of Appendix. 



