714 MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS 



European plants the epiderm consists of but a single row of cells, 

 which, moreover, are usually thin-walled ; whilst in the generality 

 of tropical species there exist two, three, or even four layers of 

 thick-walled cells, this last number being seen in the oleander, the 

 epiderm of which, when separated, has an almost leathery firmness. 

 This difference in conformation is obviously adapted to the conditions 

 of growth under which these plants respectively exist ; since the 

 epiderm of a plant indigenous to temperate climates would not afford 

 a sufficient protection to the interior structure against the ravs of a 

 tropical sun ; whilst the less powerful heat of this country would 

 scarcely overcome the resistance presented by the dense and non- 

 conducting integument of a species formed to exist in tropical 

 climates. 



A very curious modification of the epiderm is presented by 

 Rochea falcata, which has the surface of its ordinary epiderm (figs. 

 55!). 5(50, a. a] nearly covered with a layer of large prominent 

 isolated cells, b, b. A somewhat similar structure is found in 

 Mesembryanthemum crystallinum, commonly known as the 'ice-plant,' 

 a designation it owes to the peculiar appearance of its surface, 

 which looks as if it were covered with frozen dewdrops. In other 

 instances the epiderm is partially invested by a layer of scales, 

 which are nothing else than flattened hairs, often having a very 

 peculiar form ; the 'peltate scales of JElceagnus and other shrubs 

 and herbs are very beautiful objects under the microscope. In 



numerous other case-, again, 

 we find the surface beset with 

 true /Kih-s, which occasionally 

 consist of single elongated 

 cells, but are more commonly 

 made up of a linear series, 

 attached end to end. Some- 



, : , . times these hairs bear little 



glandular bodies at their ex- 

 tremities, by the secretion of 

 which a peculiar viscidity is 

 given to the surface of the leaf, 

 stem. 01- flower-stalk, as in 

 many kinds of rose, geranium. 

 .Vc. In other instances, ihe 

 hair has a glandular body at 



its base, containing a peculiar secretion; when this secretion is of 

 an irritating quality, as in the nettle, it constitutes a 'sting.' A 

 meat variety of such organs may be found by a microscopic 

 examination of the surface of the leaves of plants having any 

 kind of superficial investment to the epiderm. Many connecting 

 links present themselves between hairs and scales, such as the 

 stellate hairs of I )<'iil :'iu x<-<tli,-d. which a good deal resemble those 

 within the -iir chambers of the yellow water-lily (fig. 527). The so- 

 called -glands' 01- -tentacles' of the sundew (Drosera) are not 

 really hairs, hut out grou t hs of the internal tissue of the leaf, each 

 penetrated by a libro- vascular bundle. 



Fi<;. .">()0. Portion of vertical section of leaf 

 of Ifiir/ifii. showing the small cells, a, a, 

 of the inner layer of epiderm ; the large 

 cells, b, b, of the outer layer ; c, one of the 

 stomates; </, </, cells <>!' the parem-hyim- ; 

 L, cavity Between the |>arenchynuttous 

 cells into which the stomate opens. 



