314 THE SEED. 



Robert Brown, and were adopted as primary and tribal characters 

 by DeCandolle. 



614. As to number of cotyledons, the two types of embryo 

 are the 



Monocotyledonous, with a single cot}iedon, i. e. leaves at the 

 first nodes alternate (39) ; and 



Dicotyledonous, with a pair of cotyledons, i. e. leaves of the 

 first node in the most simple whorl, a pair, in other words, oppo 

 site (21) ; with its modification of 



Polycotyledonous (38), the leaves of the first node in whorls of 

 three, four, or more. This occurs with constancy in a majority 

 of Coniferse (Fig. 48, 49), occasionally and abnormally in sundry 

 ordinary dicotyledonous species. 



615. There are several embryos of the cot} T ledonous type in 

 which one cotj'ledon is smaller than the other, viz. the inner 

 one when the embiyo is coiled or folded. And in all the species 

 of Abronia (a genus allied to Mirabilis, Fig. 18) this cotyledon 

 is wanting, so that the embryo becomes technically monocot}'le- 

 donous. In another genus, the Dodder (Fig. 78, 79), both 

 cotyledons are constantly wanting ; and the plumule shows only 

 minute scales, the homologues of succeeding leaves reduced 

 almost to nothing. 



616. Sometimes the two cotyledons are consolidated into one 

 body by the coalescence of their contiguous faces ; when they 

 are said to be conferruminate. This occurs more or less in the 

 Horsechestnut and Buckeye (Fig. 41, 42), and is striking in 

 the seed of the Live Oak, Quercus virens. 



617. The general morphology of the embryo and its develop- 

 ment in germination were described at the commencement of this 

 volume. And so the completion of this account of plant, flower, 

 fruit, seed, and embryo brings the history round to the starting 

 point. (12-19, &c.) Having mastered the morphology and 

 general structure of the higher grade of plants, the pupil may 

 go on to the morphology and structure of cells (or Vegetable 

 Anatomy or Histology), and to the study of Cryptogamous 

 Plants in all their grades. 



