64 ANOMALOUS COTYLEDONS. [BOOK i. 



calling the two-lobed part of the embryo (Plate VI. fig. 17. c) 

 a plumule, instead of cotyledons. 



An inequality of cotyledons is the most unusual circum- 

 stance with dicotyledons, and forms a visible approach to 

 the structure of monocotyledons : it occurs in Trapa and 

 Sorocea, in which they are extremely disproportionate. In 

 Cycas they are also rather unequal; but in a much less 

 degree. 



A case has been mentioned by Mr. Griffith, in Crypto- 

 coryne spiralis, of the cotyledon being cut off, after being 

 formed. " The separation/' he says, " of the chief part of 

 that portion, which is evidently from its direction the coty- 

 ledon, is most remarkable, and forms another exception to a 

 general law. I allude to the very general absolute necessity 

 of the cotyledons. I am, however, inclined to think, from 

 this and some other instances, that the presence of a highly 

 developed plumula occasionally obviates this necessity. The 

 separation in question appears to depend upon some constric- 

 tion exerted upon the cotyledon by the apex of the nucleus/ 7 

 (Linn. Trans., xx. 271.) 



The embryo of MONOCOTYLEDONS (Plate VI. fig. i, B, &c.) 

 is usually a solid, cylindrical, undivided, homogeneous body, 

 slightly conical at each extremity, with no obvious distinction 

 of radicle, plumule, or cotyledons. In germination the upper 

 end swells and remains within the testa (fig. 10. c b, &c.) ; 

 the lower lengthens, opens at the point, and emits one or 

 more radicles : and a thread-like green body is protruded 

 from the upper part of the portion which is lengthened beyond 

 the testa. Here the portion remaining within the testa is a 

 single cotyledon; the body which lengthens, producing radicles 

 from within its point, is the cauliculus ; and the thread-like 

 protruded green part is the plumule. If this is compared 

 with the germination of dicotyledons, an obvious difference 

 will be at once perceived in the manner in which the radicles 

 are produced : in monocotyledons they are emitted from 

 within the substance of the radicular extremity, and are 

 actually sheathed at the base by the lips of the passage 

 through which they protrude ; while in dicotyledons they 



