DIVISION V. 

 ANGIOSPERMS. 



See pages 3 and 224. To this Division belong the majority 

 of the Flowering - plants. They are divided into two parallel 

 classes, the Monocotyledons and the Dicotyledons, which differ 

 from each other not only in the number of cotyledons, which, with 

 a few exceptions, is one in the former, two in the latter, but also 

 in the internal structure of the stem, the venation of the leaves, 

 the number of the parts of the flower, etc. Assuming that these two 

 classes have sprung from a common origin, it is amongst the Helobiete in the 

 first, and amongst the Polycarpicse in the second class that we might expect 

 to find closely allied forms, which might reasonably be supposed to have varied 

 less from this original type. As for the rest, they seem to stand quite parallel, 

 without exhibiting any close relationship. It is scarcely proved that the 

 Monocotyledons are the older class. 



[Our knowledge of the forms included under the Angiosperms 

 has recently been considerably increased by Treub (Ann. d. Jar. 

 Sot. 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 Angio- 

 spernis would be represented thus : 



Angiospermae. 



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. 



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