242 R. BRAITHWAITE ON THE HISTOLOGY OF PLANTS. 



Thus we find each kind of cell is constructed so as best to 

 carry on its appointed function ; where freedom and quickness of 

 circulation are required, as in the milk-vessels of such plants as 

 the sow-thistle, lettuce, and celandine, the walls are thin, and all 

 obstructing partitions are removed ; on the other hand, where 

 strength is needed, as in so many fibres used in our manufactures, 

 deposit goes on in the interior until hardly any central space is 

 left, and if firmness and resistance are required, this deposit 

 becomes so indurated as to give those qualities we value in such 

 woods as oak, mahogany, box, and ebony; while even in them 

 provision is made for interchange of air and fluids by the beautiful 

 pores and canals already referred to. 



Illustrative Figures. 

 Plate X. 



Fig. 1. — Albumen cell from Date-stone, seen under water. X 400. 

 Fig. 2. — Lignified Parenchym-cell from shell of Walnut, with 



branched pore-canals. X 660. 

 Fig. 3. — Fibre cell from wood of Finns Picea. 125. 



Fig. 4. — Ditto from bast of Larch. X 125. 

 Fig. 5. — Fibre cell from wood of Yew with bordered pores and 



spiral band, x 400. 

 Fig. 6. — Net-like perforation of partition wall of vessel in 



Lonicera caprifolhim. X 400. 

 Fig. 7. — Spirally thickened tubular cell from Dahlia. X 370. 

 Fig. 8. — Part of a so-called Scalariform vessel from Pteris 



aqmlina, p. p. the net-like perforation of the transverse 



wall. X 370. 

 Fig. 9. — Transverse partition in Cucurhita pepo. A. in longitudinal 



section, c. the cellulose case ; m. the cell membrane ; t. 



peculiar thickening ; e. contents contracted. B. in 



transverse section ; at the upper part the deposit projects 



like papillae. 

 Fig. 10. — The same from Fagus sylvatica. 



