Annual Meeting.] 136 [Mays, 
the past, and the possibility of cL'issifying them in several well- 
marked Djroups, Dr. Greenleaf explained and illnstrated the 
interpretation of various points of similarity and difference V)y 
the laws of descent with variation. Special groups were then 
studied as types, their characteristic i)oints of structure being 
quite thoroughly explained, and the class was i-ecpiested to 
construct theoretically certain possible lines of variation. With 
these as a basis of comparison, the various related families were 
studied and their relationships thus given a real meaning. 
For example, the lily family is chiefly characterized by having 
regular flowers with six parts in the perianth, six stamens, and a 
superior three-celled ovary. Four principal lines of possible 
variation are the following : — 
1. Multiplication of parts; shown well in Alismaceae,the water 
plantain family. 
2. Irregularity of parts; Pontederiaceae, the ])ickerel-weed 
family. 
3. Adnation of parts; Amaryllidaceae. 
4. Reduction in number of parts ; a. with adnation, in Iridaceae ; 
b. with adnation and irregularity, in Orchidaceae ; c. with extreme 
reduction, in Gramineae. 
These facts are of course well known to the systematic botanist, 
but they are generally considered too recondite to permit of class 
demonstration. They were not found so. On the contrary, 
their presentation was extremely simple, and the class have 
readily understooil the problems i)resented, moreover were 
awakened to an interest in the subject Avhich was wortliy of 
remark. 
Besides the exceptionally high marks and high average of 
attendance, 41 members expressed their wish to attend a course 
in continuation of the work already planned, if it be given another 
year. Moreover, several of the members found time to arrange 
their notes and specimens, accompanying them with charts and 
notes descriptive of affinity, in a manner most credital)le to their 
authors. 
The series of special courses in historical geology and jialeon- 
tology was continued by the Curator. There were sixteen lessons 
of two hours each, beginning November 4, 1892, and terminating 
March 25, 1893. The whole number of tickets issued was thirty- 
eight, and the average attendance was twenty-five. The class 
