[Our knowledge of the forms included under the Angiosperms has recently been considerably increased by Treub (_Ann. d. Jar. Bot. d. Buitenzorg_, 1891), who has shown that the Casuarinas differ in many important points from the typical Angiosperms. Among other characters the pollen-tube is found to enter the ovule near the chalaza and therefore at the opposite end to the micropyle, and Treub therefore suggests that these plants should be placed in a subdivision termed Chalazogams. According to this view the principal divisions of the Angiosperms would be represented thus:-- =Angiospermæ.= Sub-division. Sub-division. CHALAZOGAMES. POROGAMES. Class. Classes. Chalazogames. Monocotyledones, Dicotyledones. More recently Nawaschin (_Bull. Acad. Imp. Sci. St. Petersb._, ser. iii., xxxv.) has shown that _Betula_, and Miss Benson (_Trans. Linn. Soc._, 1894) that _Alnus_, _Corylus_, and _Carpinus_ also belong to the Chalazogams. Our knowledge, however, is still so incomplete that one would hesitate to accord the full systematic value which Dr. Treub attaches to his discovery until the limits of the Chalazogamic group are better defined; and it would hardly be justifiable to include the Casuarinas and the above-noted genera in one family.] Class 1. =Monocotyledones.= _The embryo has only one cotyledon; the leaves are as a rule scattered, with parallel venation; the vascular bundles of the stem are closed, there is no increase of thickness. The flower is typically constructed of five 3-merous whorls, placed alternately._ THE EMBRYO is generally small in proportion to the abundant endosperm (exceptions, see _Helobieæ_), and its single cotyledon is often sheath-like, and very large. On the germination of the seed either the entire cotyledon, or its apex only, most generally remains in the seed and absorbs the nutritive-tissue, while the lower portion elongates and pushes out the plumule and radicle, which then proceed with their further growth. The primary root in most cases soon ceases to grow, but at the same time, however, numerous lateral roots break out from the stem, and become as vigorous as the primary root, or even more so. Increase in thickness does not take place in these roots; they branch very little or not at all, and generally die after a longer or shorter time.