280 MORPHOLOGY. 



the epidermis, nothing is to be said in general terms, but that hairs are 

 infrequent on the surfaces of leaves in Monocotyledons. It is, however, 

 to be remarked, that the leaves in the bud are sometimes furnished with 

 hairs, which on further development of the organ fall away, and leave 

 scars which are sometimes mistaken for original peculiarities. Nuphar 

 luteum * offers an example of this. Hairs consisting of a cylindrical cell, 

 bearing a spherical cell above, and attached upon little indentations in 

 the epidermis which they almost cover, are still more frequent : these 

 also are frequently destroyed, and leave deceptive scars behind. The 

 epidermis in their vicinity always presents some peculiarities. Of this 

 the generality of tropical Orchidacece (Pleurothallis ruscifolia), and many 

 of the Piperacece (Piper obtusifolium\ are instances. As has been men- 

 tioned under the subject of the epidermis, some leaves present peculiarities 

 in the stomata. In Nerium, Banksia, and Dryandra, small pits clothed 

 with epidermis, beset at the edges with hairs, are found upon the leaf, 

 and it is only at the bottom of these pits that the stomata occur. In 

 Saxifraga sarmentosa and cuscutcpformis, the stomata are ranged in 

 groups, and they are set closely together. The longer diameter of the 

 stomata is sometimes turned in one way, sometimes in another. In leaves 

 proportionally very long, it is parallel to the longer diameter of the leaf, 

 as in Grasses (Liliacece, Coniferce). In some leaves, and especially in 

 fleshy ones with leathery integument, the peculiar layer of secretion as- 

 sumes a very considerable thickness, and even causes the leathery con- 

 sistence of the integument. This secreted substance is in rare cases of a 

 very soft gelatinous nature, as in Hydropeltis. Some leaves, as, for in- 

 stance, many of the species of Saxifraga, have at their edges small groups 

 of very delicate walled cells, filled with opaque contents, over which the 

 epidermis is never perfected, but persists in the original condition of epi- 

 thelium. In these groups is secreted the great abundance of carbonate 

 of lime which occurs in these plants. 



I shall speak of the development of individual cells or groups of cells 

 of the leaves into new plants further on, in connection with propagation. 



c. Complete Review of the Foliar Organs. 



133. The floral parts of a plant are here advantageously dis- 

 tinguished from all other foliar organs, and are termed flower- 

 leaves (phylla), whilst other leaves are termed true-leaves (folia 

 sensu stricto). 



1. True Leaves (Folia). 



A. Seed-leaves (cotyledons), generally round or flat, fleshy, 

 little divided, and never compound. (See under Embryo.) 



B. Stalk or stem-leaves (folia caulina f). Their forms are 

 very various, as has been shown in the foregoing paragraphs. 

 Those immediately following the cotyledons are usually simple ; the 



* Wiegmann's Archiv, Jahrg. iv. (1838), vol. L p. 51. 



f The term is allowable here. As opposed to f. radicalia it has no meaning, since 

 the root never produces leaves. 



