122 PART I. — ORGANOGRAPHY. 



There are a few instances, also, where plants whose actual 

 affinities are with Dicotyledons, possess but one cotyledon, the 

 other having become aborted, the embryos thus becoming falsely 

 monocotyledonous. This is the case with Abronia. Plants of 

 this kind should not be confounded with true Monocotyledons. 



The distinction between monocotyledonous and dicotyledon- 

 ous embryos is, with these exceptions, one of fundamental 

 importance, — one of the great divisions of the flowering plants, 

 the Monocotyledons, being characterized by monocotyledonous 

 embryos, and another, the Dicotyledons, by dicotyledonous ones. 



The individual cotyledons may be folded or bent in various 

 ways in the seed, as leaves are in the bud, and their folding may 

 be described in the same way. They also have a variety of 



Fig. 359. 



Fig. ^00. 



Fig. 358. 



Fig. 358.— Embryo of Basswood, showing lobed cotyledons. 

 Magnified. 



Fig. 359. — Diagram illustrating accumbent cotyledons. 

 Fig. 360. — Diagram illustrating incumbent cotyledons. 



shapes, the same as ordinary leaves, though they are much more 

 commonly entire. Occasionally, however, we find them toothed 

 or lobed, as in the embryo of the Basswood, Fig. 358. 



Although we often find the embryo straight, or the caulicle 

 lying in the same line as the cotyledons, in many seeds it is bent 

 so as to lie alongside of them. In this case it may be applied 

 to their edges, as shown in the diagram, Fig. 359, which repre- 

 sents a cross-section through the cotyledons and caulicle, in 

 which case it is described as accumbent ; or it may be applied to 

 the outer face of one of them, as in Fig. 360, when it is described 

 as incumbent. An illustration of the former arrangement occurs 

 in the seed of the garden Candy-tuft, and of the latter in the 

 seeds of Shepherd's Purse. 



The number of seeds produced by some plants is enormously 

 great. A single Poppy capsule, according to Cooke, has been 

 known to contain as many as forty thousand seeds, and the 



