File:Contributions from the Botanical Laboratory, vol. 11 (1934) (20500301870).jpg

Title: Contributions from the Botanical Laboratory, vol. 11
Identifier: contributionsfro11univ (find matches)
Year: 1934 (1930s)
Authors: University of Pennsylvania. Botanical Laboratory; University of Pennsylvania. Morris Arboretum
Subjects: Botany; Botany
Publisher: Philadelphia : (s. n. )
Contributing Library: Penn State University
Digitizing Sponsor: Lyrasis Members and Sloan Foundation

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680 BOTANICAL GAZETTE (JUNE -•wo/noA/oac/T/- o 1 + 1 i i s c o 6 • 7 t ^ I O 0. e ^ 5P from four healthy specimens in order to eliminate individual varia- tions as much as possible. The curve is smooth and most like that of E. pulcherrima var. oak. The isoelectric points of the two curves, however, are widely divergent. The latex particles of E. geniculata do not move in an electric field at pH 4.7, while those from E. pulcherrima var. oak are isoelectric at pH 3.9. The curve for E, heierophylla is no more closely related by its shape to E. geniculata than to the members of the E. dentata-E. pulcherrima group. Since the position of the point at pH 3.2 on the E. heierophylla curve caused most of the difference in shape between it and the curve for E. geniculata, this point was checked again and found to have the same position (within experimental error) as reported previously (10). The i.p. of particles of E. heierophylla latex was redetermined with plants grown from different seed and was again found at pH 5.1. This is not very close to that of E. geniculata. Since neither the systematic position nor the geographical distribution of these species offers a clear explanation for this divergence, it was thought that an investigation of chromosome numbers might be of value. Carano (4) reported that Poinsettia pulcherrima R. Grah. ( = £. pulcherrima Willd.) has 10 chromosomes in the haploid cells ^'con sufficiente approssimazione." The chromosomes of the other species and varieties in this section apparently have never been counted. Root tips were fixed in Nawaschin's fluid as modified by Sax (14) and dehydrated and imbedded in paraffin by means of Zirkle's n-butyl alcohol technique (17). Transverse sections were cut lo/x thick, stained in crystal violet, and destained by Newton's lodme method (11). A 15X orthoscopic ocular, a Zeiss HI 100 objective, n a I 30, and a camera lucida were used in counting and drawing. Zettnow's solution of copper sulphate and potassium bichromate diluted to one-third was used as a Ught filter. This solution gives nearly monochromatic light and makes objects stained violet appear as black The results of the counts are given in table I while figures 3-9 show drawings of typical somatic metaphase plates. The table also presents data for a hybrid, E. pulcherrima var. oak y^E Pul^ cherrima var. white, obtained from the Missouri Botanical Gar-

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