7l8 MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS 



numerous stomates, which, contrary to the general rule, are here 

 found in the upper epiderm alone. 



The examination of the foregoing structures is attended with 

 very little difficulty. Many epiderms may be torn off, by the exer- 

 cise of a little dexterity, from the surfaces of the leaves they 

 invest without any preparation ; this is especially the case with 

 monocotyledons generally, the veins of whose leaves run parallel, 

 and with such dicotyledons as have very little woody structure in 

 their leaves. In those, on the other hand, whose leaves are furnished 

 with reticulated veins to which the epiderm adheres (as is the case in 

 by far the larger proportion), this can only be detached by first 

 macerating the leaf for a few days in water ; and if their texture 

 is particularly firm, the addition of a few drops of nitric acid to 

 the water will render their epiderms more easily separable. Epi- 

 derms may be advantageously mounted either in weak spirit or in 

 glycerin-jelly. Very good sections of most leaves may be made by 

 a sharp knife, handled by a careful manipulator ; but it is generally 

 preferable to use the microtome, placing the leaf between two pieces 

 either of very soft cork or of elder- pith or carrot, or imbedding it in 

 paraffin. In order to study the structure of leaves with the fulness 

 that is needed for scientific research, numerous sections should be 

 made in different directions, and slices taken parallel to the surfaces 

 at different distances from them should also be examined. There is 

 no known medium in which such sections can be preserved altogether 

 without change ; but some one of the methods formerly described 

 will generally be found to answer sufficiently well. 



Flowers. Many small flowers, when looked at entire with a low 

 magnifying power, are very striking microscopic objects ; and the 

 interest of the young in such observations can scarcely be better 



excited than by directing their 

 attention to the new view they 

 thus acquire of the ' composite ' 

 nature of the humble down- 

 trodden daisy, or to the beauty 

 of the minute blossoms of many 

 of those umbelliferous plants 

 which are commonly regarded 

 only as rank weeds. The 

 scientific microscopist, how- 

 ever, looks more to the organi- 

 sation of the separate parts of 

 FIG. 564. Cells from petal of the flower ; and among these 



Pelargonium. } ie nnc i s abundant sources of 



gratification, not merely to his 



love of knowledge, but also to his taste for the beautiful. The general 

 structure of the sepals and petals, which constitute the perianth, or 

 floral envelope, closely corresponds to that of leaves. The petals 

 seldom contain unchanged chlorophyll ; but usually either the 

 chlorophyll in the petals (and sometimes also in the sepals) is 

 changed into a solid yellow pigment (carotin?) ; or the chlorophyll 

 lias entirely disappeared, and is replaced by a pigment, blue, red, 



