354 METHODS IN PLANT HISTOLOGY 



SO few cells between the upper and lower epidermis that it is a good 

 type for students to draw. 



Buds will furnish beautiful preparations of young leaves and, at the 

 same time, will show the vernation. Cut the bud transversely, a Httle 

 above the middle; remove the bud scales, if they promise to cause 

 trouble; retain only enough tissue at the base of the bud to hold the 

 parts in place. Fix in formalin acetic alcohol; imbed in paraffin; and 

 stain in safranin and light green. 



Epidermis, stripped from the leaf, fixed in 10 per cent formaUn in 

 water for a day or two, and then stained in safranin and light green, 

 will give excellent views of stomata. The development of stomata is 

 particularly well shown in Sedum purpurascens, even in leaves which 

 have reached the adult size. The epidermis is very easily stripped from 

 a leaf of Sedum. If the big Sedum maximum is available, pieces of 

 epidermis 6 or 7 cm. long and 2 or 3 cm. wide are easily stripped off, 

 almost free from any underlying tissue. The epidermis of Lilium and 

 Tradescantia shows fine, large stomata, but it is not so easy to strip off. 

 In these two genera the stomata, as in nearly all leaves, show only the 

 adult structure. 



Floral development. — For a study of floral development very 

 young buds are necessary, and it is best to select those forms which 

 have rather dense clusters of flowers, in order that a complete series 

 may be obtained with as httle trouble as possible. 



The usual order of appearance of floral parts is (1) calyx, (2) corolla, 

 (3) stamens, and (4) carpels; but if any of these organs is reduced or 

 metamorphosed, their order of appearance may be affected. 



Floral development is easily studied in the common Capsella hursa- 

 pastoris (Fig. 124). The best time to collect material is late in March 

 or early in April. Dig up the plant, carefully remove the leaves, and 

 in the center of the rosette a tiny white axis will be found. A series of 

 these axes from 3 to 9 mm. in length, and from 1.5 to 3.5 mm. in di- 

 ameter will give a very complete series of stages in the development of 

 the floral organs. Preparations from the apex of the shoot taken after 

 the inflorescence appears above ground are not to be compared with 

 those taken early in the season, because the pedicels begin to diverge 

 so early that median longitudinal sections of the flowers are com- 

 paratively rare. Fix in chromo-acetic acid and stain in Delafield's 

 haematoxylin. The sections should be longitudinal and about 5 m 

 thick. Capsella shows the hypogynous type of development. The or- 



