CHAPTER III. ORGANS OF PLANTS. 201 



Make similar sections and studies of the root of some herbaceous Dicotyle- 

 don, such as that of the common Buttercup, or of the American Cowslip, and 

 of some Fern, such as Osmunda cinnamomea, and observe that in all essential 

 respects the structure is the same as that of the roots previously studied. 



Now cause a few beans or peas to germinate, and make transverse sections 

 of the primary root in different stages of its development. Note that, when 

 young, its structure corresponds with the rest, but afterward it undergoes im- 

 portant secondary changes. By means of a series of sections, study the succes- 

 sive stages of these changes, recording your observations by aid of drawings. 



6. For the study of the arrangement of fibro-vascular bundles in leaves, 

 obtain the following : the fork-veined leaflets of the Cinnamon Fern or of the 

 Maiden-hair Fern ; the parallel-veined leaves of the Lily-of-the-Valley or of 

 Solomon's Seal ; and the reticulate leaves of the Wild Cranberry, of the Maple 

 and of the Wild Cucumber (Echinocystis). In order that the finer ramifications 

 of the veins may be distinctly seen, it is best that the leaves should first be 

 bleached and then stained. Soak them for a few days in alcohol to remove the 

 chlorophyll, then transfer them to Labarraque's solution, and let them remain 

 until colorless, but not so long as to cause their disintegration. They must 

 now be soaked for some time in clean water, or better, be allowed to remain 

 for some hours in running water, until the last traces of the odor of chlorine 

 have disappeared. They should then be allowed to stand for a little time in 

 water slightly acidulated with hydrochloric or nitric acid, and then transferred 

 to a very dilute aqueous solution of methyl-green and permitted to remain until 

 the veins have become distinctly stained. They may then be rinsed in clean 

 water and examined. The lignified tissues of the veins are more deeply stained 

 by this process than the rest of the structure, and the fibro-vascular system 

 may, therefore, be readily traced. Such preparations may be mounted in 

 balsam, and if the preparations are not much exposed to light, the aniline 

 stain will persist for years. 



7. For the study of the internal structure of bifacial leaves, take almost 

 any flattened leaf, like that of the Currant, Beech, or American Elm, and place 

 it between two pieces of Elder pith and make thin slices trans\ersely, with a 

 razor, transferring the sections to water as fast as made. By aid of a camel's 

 hair brush, float some of the thinnest ones upon a slide, cover with a cover-glass 

 ana examine. Observe the vertically elongated palisade cells beneath the 

 upper epidermis, the loosely arranged parenchyma farther interior, and the 

 somewhat more compactly arranged parenchyma next the lower epidermis. In 

 the lower epidermis, also, a side view of stomata may be obtained. Observe 

 that these each communicate with a large intercellular space. Study the sec- 

 tion of a vein, and observe what kind of bundle it represents, also the position 

 of the phloem, as respects the lower epidermis. 



By a similar method, the structure of centric leaves may be studied. 

 For this purpose, leaves of the Wax-plant (Hoya caruosa), or of the garden 

 Portulacca, may be used. Here, it will be observed, no distinct palisade tissue 

 is developed, and there is little difference of structure between the upper and 

 under sides of the leaf. 



Now compare with these the leaf of the common White Pine, making thin 



