FUNCTION.] OF TROP/EOLUM. 229 



from its carpel, and slight traction is made upon this cellular 

 process, the suspensor, with the embryo, may be withdrawn 

 from the embryo-sac, through the exostome and apex of the 

 nucleus ; thus proving the perfect continuit} 7 of this cellular 

 process with the suspensor, and through it with the embryo 

 itself. 



Sixth Period, The suspensor is now more attenuated, 

 consisting only, as at first, of two rows of cells ; the cellular 

 process, with which it is organically united, has reached the 

 base of the ovule ; the cells of its extremity abound in cyto- 

 blasts, showing it to be yet progressing in its development. 

 With the increased growth of the embryo two lateral processes 

 are observed proceeding, on opposite sides, from the axis and 

 evidently forming the first traces of the cotyledons. 



Seventh Period. All distinction between the nucleus and 

 its tegumentary membrane ceases, as they are now united in 

 one envelope inclosing the embryo-sac. The cellular process 

 connected with the suspensor has become so much developed, 

 that its extremity has passed around the base of the ovule 

 and is directed towards the axis of the pistil. The lateral 

 processes of the axis of the embryo have become distinct 

 fleshy cotyledons extending backwards from their point of 

 origin towards the radicle, as well as forwards in the direction 

 of the plumule ; both which organs they inclose in corre- 

 sponding depressions in their opposed surfaces. With the 

 development of the radicle towards the exostome, the opposite 

 extremity of the axis of the embryo (in the form of the 

 plumule) extends towards the base of the nucleus, but is still 

 inclosed in the depression formed in the concavity of the 

 cotyledons. 



The subsequent changes consist chiefly in the great develop- 

 ment of the cotyledons, which ultimately come to occupy the 

 whole cavity of the nucleus, filling the space usually taken 

 up by the albumen." 



Upon these facts Dr. Giraud observes, that the physio- 

 logical inferences deducible from them contribute to the 

 determination of many unsettled points involved in the 

 theory of vegetable embryogeny, and serve to elucidate many 

 obscurities relating to the morphology of the embryo. 



