THE HIGHER CRYPTOGAMIA. 357 



once, twice, or three times by septa parallel to the longitu- 

 dinal axis of the wood. Thus there is formed a mantle of 

 cambium surrounding the mass of wood on the sides and 

 from beloAv, and passing above into the growing cellular 

 tissue of the end of the bud. 



At the recommencement of vegetation in the second year 

 an active multiplication of the cells of this cambial layer 

 begins. The increase in size keeps pace with the growth 

 in thickness of the new portion of the stem produced by the 

 development of the terminal bud. The multiplication of 

 the cambial cells is most remarkable at the sides of the 

 mass of wood ; it is less vigorous in that half of the cam- 

 bium which surrounds the lower, half-moon-shaped portion 

 of the woody mass. 



The development of the cambium has pushed outwards 

 the cortical tissue which is filled with assimilated matter. 

 The vascular bundles are thereby much stretched, but not 

 so as to destroy them. The vitality of the cells of the 

 vascular bundles manifestly still exists ; by the expansion 

 of their own walls they follow the change of position of the 

 surrounding tissue. The thickenings of the walls of the 

 vessels are alone materially changed during these processes, 

 being loosened here and there and in other places distorted, 

 so that every trace of regular arrangement disappears (PI. 

 LXI, fig. 3). The function also of the vascular bundle does 

 not seem to have come to an end at the time of the com- 

 mencement of the vegetative period which succeeds its 

 formation. The starch and oil contained in the cells of the 

 bark of the previous year which bark has been pushed 

 outwards are gradually sucked up and carried to the grow- 

 ing portions of the plant. At the end of each vegetative 

 year the cells of the bark of the preceding year contain only 

 a transparent fluid. 



The old bark which is pushed outwards, gradually dies 

 from the periphery inwards ; its cell-walls assume a deep 

 brown colour, and ultimately the bark perishes. The new 

 bark behaves similarly to the old bark, in the fact that the 

 cells of the portion which clothes the furrow of the stem 

 only expand slightly in breadth. The indentation of the 

 stem already appears deeper than in the preceding year, on 



