LEAF AND FLOWER. 15 



III. THE LEAF. 



The leaf presents few difficulties in histological manipulation 

 For all necessary details consult pp. 155-164. The following 

 plants atford excellent material for study : 



Of the centric arrangement of parenchyma in the blade, Trit- 

 icum vulgare, Acorns, and many of the Cactacese. 



Of the bifacial arrangement of parenchyma, many plants with 

 flat horizontal leaves. 



IV. THE FLOWEK. 



It is assumed that the student has thoroughly familiarized 

 himself with the morphology of the simpler flowers as explained 

 in Volume I., and has acquired some facility in examining, as 

 there directed, those of more complicated structure. 



The study of the microscopic anatomy of all the floral organs 

 in their adult state should precede any attempt to examine their 

 development. Since the flower should be examined in all stages 

 of its development, it is well to select for study only those flow- 

 ers which can be readily obtained in large numbers, and further- 

 more, by preference, those which are not thickly covered with 

 hairs. The common weeds Lepidium Virginicum and Capsella 

 Bursa-pastoris afford excellent material for the study of the 

 flower and its development, and have the signal advantage of 

 being much alike in the most essential respects, yet possessing 

 minor differences which are not likely to be overlooked. 



An exhaustive examination of the histology of the organs of 

 the flower should begin with the study of the sepals, the other 

 organs being taken up in their turn, and the following points 

 receiving special attention : (1) the possible occurrence of stom- 

 ata upon all the parts of the blossom ; (2) the peculiarities in 

 the proper epidermal cells of the petals ; (3) the character of the 

 parenchyma in all parts of the flower, and all differences in the 

 nature of the cell contents, notably the plastids ; (4) the charac- 

 ter and the distribution of the fibro-vascular bundles in their 

 course from the pedicel to their ultimate attenuated ramifications 

 in the several organs. 



Stamens. The character of the pollen demands special atten- 

 tion, and its examination should be followed by a comparison 

 between as many kinds as possible taken from various flowers. 

 The character of the integuments and the contents of the grains 

 should also be demonstrated. 



