No. 466.] STUDIES ON PLANT CELL. VIII. 709 



logical independence of the chromosomes. Miss Merriman 

 reports the origin of the nucleoli as masses among the meshes 

 of chromatin from which they draw their substance. TMafio, in 

 contrast to Wager, holds that the nucleoli appear as globules 

 independent ot the chromatin network and later flow together 

 into a single body. The chromosomes are also believed by 

 Mano to be morphologically independent of the nucleolus and 

 if the latter furnishes material to the former it is not by the 

 emergence of strands as described by Wager. Mano then holds 

 the nucleolus to be an accessory structure without morphologi- 

 cal relation to the chromosomes. 



The theory of the individuality of the chromosomes is of 

 course vitally concerned with the problem of the morphology of 

 the nucleolus but this topic we have reserved for later treatment 

 under the caption : " The Essential Structures of the Plant Cell 

 and their Behavior in Ontogeny." The chromatin and nucleoli 

 within the nucleus of a higher plant lie in a vacuole whose fluid 

 content is bounded by a plasma membrane similar to that around 

 any vacuole in the cell. Lawson (: 03) and Gregoire and 

 Wygaerts (:O3) have emphasized this structural condition in 

 recent papers but the central idea seems to be an old one run- 

 ning through the writings of Strasburger from an early period. 



We bring up these striking conceptions of nuclear structure 

 in the higher plants because it seems very probable that a much 

 clearer understanding of the problems will come through inves- 

 tigations upon the simpler conditions in the lower plants. 

 There, we may hope to find evidence of the primitive forms of 

 nucleolar and chromatic associations with perhaps some clues as 

 to the manner of the development of the higher types of struc- 

 ture. Thus the yeast cell, as reported by Wager ('98) with its 

 chromatin sometimes collected within a vacuole and sometimes 

 distributed in the cytoplasm and a nuclear body (nucleolus) in 

 close association with the nuclear vacuole, but not within, is of 

 the greatest interest as presenting intermediate stages in the 

 complexity of nuclear structure and illustrates what may be 

 hoped from further research among the lower forms. 



The Chromatophore and Plastid. In considering the great 

 variety of chromatophores and plastids exhibited among the 



