400 FORAMEN. [BOOK i. 



that, to give an exact idea of it, I would compare it not to a 

 hole, as those express themselves who have hitherto spoken 

 of the exostome and endostome, but to the mouth of a goblet 

 or of a cup. It may therefore be easily understood, that, 

 to perceive either the secundine or the nucleus, it is not 

 necessary to have recourse to anatomy. I have often seen, 

 most distinctly, the primine and secundine forming two large 

 cups, one of which encompassed the other without entirely 

 covering it, and the nucleus extending itself in the form of 

 an elongated cone beyond the secundine, to the bottom of 

 which its base was fixed/' 



In practical botany the detection of the foramen is often 

 a matter of great importance ; for it enables an observer to 

 judge from the ovule of the direction of the radicle of the 

 future embryo : it having been ascertained by many observa- 

 tions that the radicle of the embryo is almost always pointed 

 to the foramen. A partial exception to this law exists, how- 

 ever, in Spurgeworts (Euphorbiacese), in many of which Mirbel 

 has noticed that, after fertilisation, the axis of the nucleus 

 and the endostome are inclined five or six degrees, without 

 the exostome changing its position; by this circumstance 

 the foramen of the secundine and that of the primine cease 

 to correspond, and the radicle, instead of pointing when 

 formed to the exostome, is directed to a point a short distance 

 on one side of it. 



Mr. Griffith has pointed out an example of departure from 

 this law, in Cryptocoryne ciliaris (Linncsan Transactions, vol. xx) . 

 This exception, however, he regards as being corroborative of 

 the validity of the law, since in the earlier periods of deve- 

 lopment the direction of the embryo is not only rectilinear, but 

 the radicle corresponds exactly with the apex of the nucleus, 

 and with the foramen. He would limit the expression of the 

 law to " radicle pointing or corresponding to the apex of the 

 nucleus," since there are exceptions to its correspondence 

 with the foramen. " Another circumstance is likewise to be 

 kept in view, viz. that the law is applicable only to the direc- 

 tion of radicles of embryos, which remain inclosed in the 

 original nucleus, or in some modification of its original 

 form." 



