PRELIMINARY INQUIRY INTO THE NATURE OF THE CELL. 



3 



this time relatively very large (/c). The cell-sap first appears, when the cell is grow- 

 ing quickly {£), in the form of drops ( Vacuoles) in the interior of the protoplasm 

 {B, s); at a later period these drops usually coalesce, and form a single sap-cavity 

 (C, s), which is enclosed by the now sac-like hollow substance of the protoplasm. 



In their earliest state the cells of the wood and cork of trees show conditions 

 of development which correspond essentially to those represented in Fig. i. In 

 these cells, however, a new condition follows very soon after the appearance of the 

 cell-sap; the protoplasm containing the nucleus disappears, leaving the cell-cavity 

 filled either with air or with water. Older wood and cork thus consist of a mere 

 framework of cell-walls. 



An important difference exists between the further behaviour of those cells 

 which enclose protoplasm, and of those from which it has disappeared. The former 

 only can grow, develope new chemical combinations, and, under certain conditions, 



Fig. 2. — Sexual reproduction oi Fucus vesiculosiis ; A branclied hair bearing antheridia ; 5 antherozoids ; / an oogonium C^^ with 

 paraphyses / ; // the exterior membrane a of the oogonium is split, the inner membrane i protrudes, containing the oospheres ; III an 

 oosphere escaped, with antherozoids swarming round it ; V first division of the oospore or fertilised oosphere ; IV a young plant 

 resulting from the growth of the oospore {after Thuret, Ann. des Sci. Nat. 1854, vol. 11). (/9 x 330 ; all the rest X 160.) 



form new cells. The latter are never capable of further development; in the case 

 of wood, they are of service to the plant only from their firmness, power of absorbing 

 water, and peculiar form; in cork, by forming protecting envelopes which surround 

 the living succulent cellular tissue. 



Since then no further development can take place in cells which no longer 

 contain protoplasm, it may be concluded that the latter is the proximate cause of 

 growth. We shall see hereafter that the development of each cell begins with 

 the formation of a protoplasm-mass, and that the cell-wall is also generated from 

 it; but the relation of the protoplasm to cell-formation is, still more striking when 

 it exists for some time in the free state as a mass of definite form, which eventually 

 clothes itself again with a fresh cell-wall, and takes up cell-sap. We have an 

 excellent example of this in the reproduction of the Fucaceae. On the fertile 

 branches of these large marine Algse, of which we may take Fucus vesiculosus as 



B 2 



