84 



HUTCHINSON'S POPULAR BOTANY 



duce fresh tissue. These 

 actively dividing cells have 

 thin walls, and no spaces be- 

 tween the cells : they are rich 

 in protoplasm, and always con- 

 tain a nucleus. From cells 

 of this kind all permanent 

 tissues originate. They are 

 found, therefore, only in the 

 growing parts of plants, as 

 buds, the apex of roots, and 

 in certain parts of the stem. 

 Even sclerenchyma originated 

 in meristem. 



Special cells or groups of 

 cells, so disposed as to form 

 cavities in the tissue, are en- 

 gaged in the formation of 

 the degradation- and by-pro- 

 ducts (p. 56), and to these the 

 name of glands has been 

 given. Thus we have resin- 

 glands, oil-glands, camphor- 

 glands, honey-glands, and 

 others that need not be par- 

 ticularized. They abound, for 

 instance, in the rind of the 

 orange and lemon, the odour 



and flavour of which are derived from minute drops of volatile oil 

 stored up in vast numbers of these little cavities. Glands are frequently 

 external organs, and may be borne upon the ends of hairs, which are 

 then called glandular hairs. We find them, for example, in the Chinese 

 Primula. The margins and upper surface of the leaves of our English 

 Sundews (Drosera rotwndifolia and D. intei^media) are provided with delicate 

 glandular tentacles (loosely called " hairs " in many text-books), which are 

 veritable insect-traps. The glands have the appearance of tiny dewdrops, 

 but exude a viscid secretion, by which the thirsty and deluded visitors 

 to the plant are caught and retained for a purpose which will be explained 

 in the next chapter. 



The various kinds of vessels and permanent tissue ma} 7 be conveniently 

 classed under three heads, which are easily remembered, the arrangement 

 being quite natural. If you take any ordinary leaf say, the leaf of a Lime 

 you will perceive that it consists of a thin outer skin, enclosing some 

 tough net-like veins and a lot of soft tissue which fills up the spaces between 



Photo J>y] [E. Step. 



FIG. 116. CONE OF CEDAR-TREE (Cedrus libani). 



A very hard and solid cone of a purplish-brown tint. The scales 



are thin, and overlap tightly. The seeds take about three years 



to ripen. Natural size. MOUNTAINS OP STRIA. 



