996 3Iarq«ette, Manifestation of polarity in plant cells which usw. 



between the ehloroplasts and spindles for tlie cells are long and 

 narrow so that the ehloroplasts must necessarily oceupy this position 

 if each daughter cell is to reeeive one of them. 



The ehloroplasts of the epidermal assimilatory cells of the 

 foliage leaves of Selaginella investigated by Haberlandt 1 ) are also 

 of interest in this connection. These cells usnally have a Single, 

 large, bowl-shaped chloroplast placed at one end of the cell with 

 its coneavity in which the nncleus lies turned towards the inferior 

 of the cell. [Jnfortunately there are no data concerning the 

 behavior of this chloroplast during cell division. 



An Observation of Eosen's 2 ) on the root cap cells of Oleandi" 

 nodosa should also be mentioned here. He found in these cells 

 two more or less kidney shaped bodies lying close to the nucleus, 

 at opposite sides of it. Eosen regarded these bodies as possibly 

 tannin masses; he gives no Information concerning their behavior 

 during nuclear division. 



As relatively large bodies in the cytoplasm which undergo 

 definite changes of position during cell division, the polar struetures 

 of Isoetes call to mind some observations of Conklin's 3 ) on the 

 dividing eggs off various gasteropods and aseidians. Conklin finds 

 a diferentiated mass. the sphere substance, lying at one side of 

 the nnclens distinguished in color and density from the remaining 

 cytoplasm, and derived from the polar material of preceding 

 divisions. For a few cleavages this mass divides into two and 

 the halves migrate to the spindle poles so that they are distributed 

 to the daughter cells. In later cleavages. however, these masses 

 in the cytoplasm do not divide as the cell divides and some of 

 the daughter cells reeeive the entire mass while others reeeive 

 none. In this way a visible differentiation of the cells in the early 

 cleavage stages is brought about, a differentiation which is 

 associated with the later differentiation of tissues in the embiyo. 

 It seems that these masses of sphere substance are not definitely 

 bounded cell organs, but merely aggregations of material of different 

 composition than the remainder of the cytoplasm. 



Finally, the elaioplasts should perhaps be mentioned. The 

 elaioplasts are cell-organs presumptively concerned with the 

 produetion of oily substances and aecording to Zimmermann 4 ) are 

 of wide spread oecurrence in the plant kingdom. Usually, although 

 there are exceptions, there is a Single elaiopiast in a cell, lying 



i ) Haberlandt: DieChlorophyllkörperderSelaginellen. CFlora. 1888. p.291.) 

 Über die Plasraahaut der Chloroplasten in den Assimilationszellen von Selaginella 

 ^lartensii Spring. (Ber. d. Deut. bot. Ges. Bd. XXIII. 1905. p. 441.) 



2 ) Beiträae zur Kenntnis der Pflanzenzelle. (Cohn's Beitr. z. Biol. d. 

 Pflanzen. Bd. VII. PI. in. Fig. 18.) 



s ) C'onkli n . E.: Karyokinesis and cytokinesis in the maturation, fertilization. 

 and cleaTage of Crepidula and other gasteropoda. (Jour. Acad. Xat. Sei. of 

 Phila, 2nd. Ser. Vol. 12. Pt, I. 1902.) The origin and cell-lineage of the 

 Ascidian egg. (Ibid. Vol. 13-.Pt. I. 1905.) 



i ) Zimmermann. A. : Über die Elaioplasten. (Beitr. z. Morph, u. Physiol. 

 d. Pflanzenzelle. 1893. p. 185. ) Elaioplasten. Elaiosphaeren und verwandte 

 Körper. (Beihefte z. bot, Ztblt. Bd. 4. 1894. p. 165.) 



