296 
METHODS IN PLANT HISTOLOGY 
the bundle transversely so that about 5 mm. of the bundle will 
project beyond the tied portion. Dip in melted paraffin, as already 
suggested for Pinus, fasten the tied portion in the sliding microtome, 
and cut with the knife placed obliquely. About 15 to 20 p is a good 
thickness for general leaf structure. In case of large leaves, cut 1 cm. 
wide and 3 cm. long and tie them together to make a good bundle for 
cutting. 
Of course, for the finest preparations, imbed in paraffin. The 
common lilac, Syringa, has a good leaf to illustrate palisade and spongy 
parenchyma; the privet, Ligustrum , is also excellent. 
Buds will furnish beautiful preparations of young leaves and, at 
the same time, will show the vernation. Cut the bud transversely, 
a little 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 alcohol and stain in 
safranin and light green. 
Epidermis stripped from the leaf, fixed in 10 per cent formalin 
in water for a day or two, and then stained in safranin and anilin 
blue, 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 show 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 little 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 
bursa-pastor is. 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. 
