IGG R. BRAITIiWAITE ON THE HISTOLOGY OF PLANTS. 



transverse sections of the roots of the common pine, and apply 

 any of the endosmotic reagents, we may observe the various 

 stages. 



The division commences by a folding-in of the primordial mem- 

 brane ; the partition of the cambial wall (not consisting of cellulose) 

 proceeds at the same time over the whole membrane ; after which 

 the mother-cell is quickly resorbed and converted into intercellular 

 substance. 



In deciduous trees multiplication of cells proceeds in the same 

 way, but those forming vessels extend rapidly, and attain their 

 normal size before other tissues. 



Cell Division, with Subsequent Partition of the Cell case. — Bi- 

 partition of the second type may be studied most completely in the 

 filiform Algfe, as we may keep the specimens in shallow troughs 

 constantly under observation, and of these Cladophora glomerata 

 is a suitable example. 



If we place a small portion under the microscope, and carefully 

 examine the terminal cell of a branch, we often find that division 

 has already commenced, for such cells are twice the length of the 

 others. The first thing we notice is, that two clear spots near the 

 middle of the cell stand away from the margin, and this is caused 

 by a collection of colourless protoplasm ; then the primordial mem- 

 brane of the mother-cell, more active at this point, folds inward 

 like a ring, which, gradually advancing, laces in the contents in 

 two halves belonging to both daughter- cells ; this infolding is most 

 distinct in slow growing plants, cultivated indoors. Immediately 

 after the infolding of the primordial membrane begins, the division 

 of the cellulose case commences, and advances continuously with 

 the infolding, so that soon after complete division the daughter- 

 cells have also acquired a delicate but distinct cellular case. 



A cementing intercellular substance appears where the part of 

 the mother-cell case, cut oft* between the cross -walls, has become 

 nearly dissolved. The application of endosmotic reagents gives us 

 a clearer view of these details. A triangular intercellular space is 

 seen at the junction of the daughter-cells, which is most distinct 

 in the slow-grown specimens, for in luxuriant tufts the primordial 

 membrane'and young cellulose case become pressed together and 

 to the mother case, and this space almost entirely disappears. 



This accounts for the error of Pringsheim and Von Mohl, that 

 in the commencing infolding of the primordial membrane a cellulose 



