338 



DICOTYLEDONOUS EMBEYO. 



they become verticillate. This occurs in Coniferse, especially in the 

 Pir (fig. 604), Spruce, and Larch, in which six, nine, twelve, and even 

 fifteen have been observed. In such cases it is probable that the 

 cotyledons are split by collateral chorisis, and thus divided into 

 several. They are linear, and resemble in their form and mode of 

 development the clustered or fasciculated leaves of the Larch. Plants 

 having numerous cotyledons are occasionally denominated polycoty- 

 ledonous. Duchartre thinks that the multiple cotyledons of the Pirs 



Fig. 604. 



are not verticillate, but occur in two opposite groups, placed like two 

 ordinary cotyledons. Hence he considers the plants to be truly 

 dicotyledonous, with the cotyledons deeply divided into a number of 

 segments. Between the two cotyledons there is a slit which is well 

 seen in Pkius Pinaster and excelsa. Thus, the arrangement of the 

 cotyledons follows the same law as that of the leaves in dicotyledonous 

 or exogenous plants, being opposite or verticillate according to the 

 mode of formation of the axis. In Welwitschia there are two coty- 

 ledons which last throughout its life (more than a century), and in the 

 course of time they grow to an enormous size, being sometimes six 

 feet long and two or three in breadth. They constitute the only 

 leaves of the plant. In species of Streptocarpus the cotyledons are 

 also permanent and act the part of leaves. One of them is frequently 

 largely developed, while the other is small or abortive. 



The texture of the cotyledons varies. They may be thick, as in 

 the Bean, exhibitiag only slight traces of venation, with their fiat 

 internal surfaces in contact, and their backs more or less convex ; or 

 they may be in the form of thin and delicate laminae, flattened on both 



Fig. 602. Embryo of Hirsea Salzmanniana, cut vertically, to show^the inequality of the two 

 cotyledons, one of which, c, forms almost the whole mass of the embryo, c*, The small coty- 

 ledon, g, Gemmule or plumule, r, Eadicle. Fig. 603. Bmbiiyo of Carapa guianensis, cut 

 vertically to show the union of the cotyledons, the distinction between which is only 

 indicated by a faint line, o. r, Eadicle. g, Gemmule. Fig. 604. Embryo of Fii. 1, 

 Taken from the seed. 2, Beginning to germinate, r, Eadicle. c. Cotyledons, which are 

 numerous ; the plant being polycotyledonous. 



