LEAF AND FLOWER. 15 



III. The Leaf. 



The leaf presents fe\y difficulties in histological manipnlation. 

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

 plants atToi'd excellent material for studj' : — 



Of the centric arrangement of parenchj-ina in the blade, Trit- 

 icurn vulgare, Acorus, and many of the Cactaceaa. 



Of the bifacial arrangement of parenclyma, many plants with 

 flat horizontal leaves. 



IV. The Flower. 



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 facilitj' in examining, as 

 there directed, those of more complicated structure. 



The stud}' 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 stud}' onlj- those flow- 

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

 more, bj' preference, those which are not thickl}' 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 niucli alike in tlie 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 

 parench3'ma in all parts of the flower, and all diff'erences 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. 



