18 



round, but still slio-litly oval in outline. In the case of 

 the ilat frond, they are usually elongated in a transverse 

 direction and ])arallel to the two flat surfaces. There is 

 no diiference to he noted in the other tissues. 



I have already referred to the growing point. It is 

 that part of the plant where the formation of new cells i-i 

 going on most actively, but it is, strictly speaking, not 

 the only part of the plant which is groAving. Cell division 

 is going ou very rapidly in this region, as may be seen by 

 looking at the size of the cells. The formation of new 

 cells is, however, not confined to this region, but is also 

 going on, though probably less rapidly, at the tips of 

 nearly all the assimilating cell rows. The innermost cells 

 of these rows gradually become collecting cells, and new 

 rows of assimilating cells are formed by branching. Xew 

 cells may also, though rarely, be formed by short tube- 

 like cells growing out from older condiicting cells. Thus 

 far the formation of new cells, as pait of the process by 

 which Chondrus crlspus grows, has been described. 



The growth in length of the shoot is brought about by 

 the cells of the conducting tissue becoming more elongated, 

 by the collecting cells becoming larger and in the end 

 passing into conducting tissue, finally by the assimilating 

 cells gradually passing into the collecting cells and new 

 assimilating cell rows being formed hj the branching of 

 the older ones. 



The cells of the conducting tissue measure about 8-10/x 

 in length at a point about lOOyw back from the shoot apex, 

 at further intervals of 100/x they increase on the average 

 to 10-14^, 20^, 30-40//, 50^, being finally 80// at 

 a distance of about 800// from the apex. 



The collecting cells, with a measurement of 4-8// in 

 their longest diameter at a distance of 100// from the 

 apex, increase at intervals of 100// to 8-10//, 10-12//, 



