INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 305 



attaclied to the part played by the nucleus in the division of vegetable 

 cells. 



The development of the two new nuclei proceeds very rapidly in 

 Tradescantia. Even while separating from one another the rods 

 begin to coalesce, the process commencing at one extremity and 

 advancing to the whole length, a longitudinal striation remaining 

 visible for about half an hour. As soon as this disappears the young 

 nuclei have a speckled appearance ; but soon a definite separation 

 takes place of the substance of the nucleus from the cell-sap, indi- 

 cated by a distinct black punctation. In three-quarters of an hour at 

 most from the time when the barrel begins to divide, the new nuclei 

 have assumed their permanent character. 



The young completely formed nuclei are at once sharply differ- 

 entiated from the hyaline substance of the cell-threads, which is in 

 the living condition altogether homogeneous. A few small vacuoles 

 make their apjiearance between the young nuclei and this substance ; 

 while at the spots where the connection is, still maintained the con- 

 tour of the nucleus soon again disappears, and the substance of the 

 cell-threads is clearly taken up into the nucleus. The young nucleus 

 hence grows rapidly, and approaches on both sides the new division- 

 wall. As soon as the absorption is completed, each of the two nuclei 

 has again a sharp contour, and retires from the division-wall to the 

 interior of the cell. The starch-grains, which resemble nucleoli, at 

 the same time make their appearance in the nucleus. 



The mature nucleus situated in the interior of the cell is suspended 

 in but a small amount of protoplasm. Only at the apex of the termi- 

 nal cell of the hairs of Tradescantia is found any considerable collec- 

 tion of protoplasm. 



The reagents found to be best adapted for these observations are 

 alcohol and 1 per cent, chromic acid ; the latter causing least change 

 in the object. The investigations were carried out in a moist 

 chamber. On the covering-glass was placed a drop of 1 per cent, 

 solution of sugar, which was spread out, and the entire freshly 

 gathered stamen placed on it, care being taken that the hairs are 

 immersed in the fluid. The covering-glass is then turned over, and 

 placed with its edges on a papier-mache frame. In the suspended 

 drop a number of hairs are sufiiciently close to the covering-glass to 

 allow of their stiidy with Zeiss's immersion system I, a magnifying 

 power of 550 with eye-piece 2. 



Structure of the Aerial Roots of Orchids.* — The aerial roots of 

 epiphytal orchids are clotlicd with a special tissue of peculiar struc- 

 ture to wliich the term velamen has been given. Of this tissue M. 

 Prillieux has made a special study, and gives the following descrip- 

 tion. 



It may be divided into two strata : — (1) the spongy envelope, 

 occupying more than half the diameter of the root, and composed of 

 10-15 or more layers of cells ; (2) the protective layer, never more 

 than one cell in thickness. 



♦ ' Hull. Snr. Hot. Ki;mc<.' xxvi. (ISTK) p. 275. 

 VOL. Ill, X 



