After an examination of the literature on chromosome counts had revealed the fact that in most instances the chromosome numbers of latesummer-flowering angiosperms are unknown. this study was undertaken. During August and September, 1933, numerous species were collected and prepared for examination. The following Compositae were among those examined:Ageratum Houstonianum Mill., Eupatorium pur pureum L., E. urticaefolium Reichard, Erigeron canadensis L., Ambrosia trifida L., A. artemisiifolia L., Heliopsis helianthoides (L.) Sweet, Helianthus grosseserratus Martens, Gaillardia aristata Pursh, Chrysanthemum Leucanthemum L. var. pinnatifidum Lecoq. and Lamotte, Sonchus oleraceus L., and Lactuca scariola L. var. integrata Gren. and Godr.
MATERIAL AND METHODSMaterial was fixed in Carnoy's fluid (6 parts 9S per cent alcohol, 2 parts chloroform, 2 parts glacial acetic acid). The young buds were left in this fixative about one hour, washed in 9S per cent alcohol, and imbedded in paraffin after clearing with cedar oil.Sections were cut from I2-IS II. in thickness, mounted serially, and stained in Delafield's haematoxylin. The stain was diluted, using I part of stain to 3 parts ordinary tap water, and the sections were allowed to remain in this solution from one to two hours. They were washed in running water for 20 minutes and then transferred to acid alcohol (one drop of hydrochloric acid to two hundred cc. of 70 per cent alcohol) to remove the excess stain. The material was examined under the microscope in order to determine the amount of stain in the tissue. When properly destained, they were placed in ammonia alcohol for a short time, dehydrated, and mounted in Canada balsam in the usual manner.
OBSERVATIONSThe chromosome counts herein reported were made in part from nuclei in diakinesis, and in part from polar views of heterotypic or homoeotypic equatorial plates in the microspore mother cells.