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METHODS IN PLANT HISTOLOGY 
The common dandelion, Taraxacum officinale, affords an excellent 
series with little labor. Examine vigorous plants which have, as yet, 
no flowers or buds in sight. Dig up the plant and dissect away the 
leaves. If there is a white cluster of flower buds, the largest not 
more than 4 mm. in diameter, cut out the cluster, leaving only enough 
tissue at the base to hold the buds in place. Larger heads should be 
cut separately. 
Our most common thistle, Cirsium lanceolatum, shows the floral 
development with unusual clearness, but the preparation of the 
material is somewhat tedious. The involucre, which is too hard to 
cut, must be carefully dissected away. Retain only enough of the 
receptacle to hold the developing florets in place. A series of sizes 
with disks varying from 3 to 10 mm. in diameter will show the 
development from the undifferentiated papilla up to the appearance 
of the archesporial cell in the nucellus of the ovule. The Canada 
thistle, Cirsium arvense, is equally good, but it is more difficult to 
dissect out the desirable parts. In the common sunflower, Helian- 
thus annuus, the young floral parts, like the mature head, are so very 
large that a satisfactory study may be made with a low-power objec¬ 
tive. As in the case of the thistle, the involucre must be trimmed away 
and only enough of the receptacle retained to hold the florets together. 
Erigeron (we have cut E. philadelphicus and E. annuus) furnishes 
a beautiful example of epigynous floral development, and the heads 
are so densely clustered that, in a single section, one may find various 
stages from heads with undifferentiated disk up to heads with florets 
showing pappus, corolla, stamens, and carpels. 
Spermatogenesis.—The earlier stages in spermatogenesis will 
be found in the preparations of floral development. The origin of 
the archesporium, the origin of sporogenous tissue, and the formation 
of the tapetum are beautifully shown in longitudinal and in transverse 
sections of the anthers of Taraxacum and many other Compositae. 
Transverse sections of the head of Taraxacum or any similar head 
at the time when pollen mother-cells are rounding off in the center of 
the head, will show various stages from the mother-cells in the center 
to the tetrads of spores at the periphery. Transverse sections of 
the anther of Polygala give exceptionally well-defined views of the 
archesporial cells and sporogenous areas. 
Lilium, Trillium, Galtonia, Iris, Tradescantia, Vida, and Podo¬ 
phyllum can be recommended for demonstrating the nuclear changes 
