OF THE UNIMPREGNATED OVULUM. 441 



lastly, that at the apex of the nucleus the radicle of the 

 future Embryo would constantly be found. 



On these grounds my opinion respecting the Embryo 

 of Cephalotus was formed. In describing the ovuhun 

 in this genus, I employed, indeed, the less correct term, 

 " sacculus," which, however, sufficiently expressed the 

 appearance of the included body in the specimens ex- 

 amined, and served to denote my uncertainty in this case 

 as to the presence of the inner membrane. 



I was at that time also aware of the existence, in several 

 plants, of a foramen in the coats of the Ovulum, always 

 distinct from, and in some cases diametrically opposite to> 

 the external umbilicus, and which I had in no instance 

 found cohering either directly with the parietes of the Ova- 

 rium, or with any process derived from them. But, as I 

 was then unable to detect this foramen in many of the 

 plants which I had examined, I did not attach sufficient 

 importance to it ; and in judging of the direction of the 

 Embryo, entirely depended on ascertaining the apex of 

 the nucleus, either directly by dissection, or indirectly from 

 the vascular cord of the outer membrane ; the termination 

 of this cord affording a sure indication of the origin of the 

 inner membrane, and consequently of the base of the nu- 

 cleus, the position of whose apex is therefore readily de- im 

 termined. 



In this state of my knowledge the subject was taken up 

 in 1818, by my lamented friend the late Mr. Thomas 

 Smith, who, eminently qualified for an investigation where 

 minute accuracy and great experience in microscopical ob- 

 servation were necessary, succeeded in ascertaining the very 

 general existence of the foramen in the membranes of the 

 Ovulum. But as the foramina in these membranes invari- 

 ably correspond both with each other and with the apex of 

 the nucleus, a test of the direction of the future Embryo was 

 consequently found nearly as universal, and more obvious 

 than that which I had previously employed. 



To determine in what degree this account of the vege- 

 table Ovulum differs from those hitherto given, and hi some 

 measure, that its corectness may be judged of, I shall pro- 



