48. FLOWERING PLANTS. 
have lost their protoplasmic contents, and that they are of use 
to the plant chiefly owing to 
the mechanical properties of 
their cell-walls. 
(c) Sometimes, instead of 
cork, the cell-walls become 
cuticularised (Lat. cuts, skin.) 
In this condition they are 
still protective, for a thick 
cuticle is almost impermeable 
‘to water. The epidermis of 

Fig. 14.—Siice or Borrie-Cork. 
c.w, cell-wall ; ¢.c, cell-cavity. 
| Zz. A 
of Xerophytes, shows this very | 
well (Fig. 43). | 
The changes that take place in 
a row of cells lead to the formation 
of vessels. If a number of cells (as 
in Diagram I. of Fig. 15) occur one 
above the other, and the cell-walls | 
which touch each other gradually |, | | . 
become thinner and thinner and ulti- 
mately disappear, then the cavities — lle. 
of the cells will communicate with | | ) 
each other and a vessel will be 
formed, as in Diagram Il. It is .=22 ae 
vessels for the most that have ligni- Fic. 15.—D1acram sHow1NG 
fied walls. The thickening of the : Sete eae oun 
cell-walls of vessels may be laid Lower eis, IL tor a 
down in various ways—sometimes which cell-walls are absorbed ; 
spirally, or in rings, or like the es ve aE ace 
steps of a ladder, so that there is a tween adjacent cells; cw’, 
considerable variety of vessels, as °e!l-wall absorbed ; c.!, cell- 
: wall perforated. 
will be seen in the next chapter ; 
sometimes the cell-walls between the cells do not entirely 
disappear, but are merely perforated with holes, so that 
cw! 
ae 
. S Loe cs 
some leaves, more especially those 
lew 


