Origin and Development of the Vegetable Embryo. 55 



namely, that in his numerous investigations he has never found 

 more than one pollinic filament within the nucleus, although he 

 has several times met with two embryonal vesicles, and conse- 

 quently two embryos fertilized by a single tube. 



Prof. Von Mohl* has published an account of his elaborate in- 

 vestigations on this subject made during the spring of 1847, his 

 attention having been newly directed to it by the observations of 

 Amici above-related. They agree almost perfectly with the latter, 

 but considering the interest attaching to the inquiry, it may be 

 as well to give an account of the points not fully described by 

 Prof. Amici, and the slight discrepancies which exist between the 

 accounts given by the two observers. 



Prof. Von Mohl states that the pollen-tubes are easily distin- 

 guished from the cells of the conducting tissue of the style by 

 their greater length and their much smaller diameter ; that of 

 the pollen-tubes being on an average y^th of a millimetre, that 

 of the cells of the tissue of the style g\jth ; and he states that the 

 " mucous tubes" of Mr. Brown are certainly the pollen-tubes. 



About the fourth to the sixth day the ovary has become twice or 

 thrice as large as at the time of the expansion of the flower ; the 

 ovule has become greatly inclined, and the coats of the ovule have 

 grown, the inner some distance upward on the nucleus, the outer 

 not so far as the inner. The nucleus has become enlarged up- 

 ward in a clavate form ; the embryo-sac is relatively much in- 

 creased in size, so that the cells which form the outer layer of 

 the nucleus are flattened, and form a comparatively thin invest- 

 ment to the embryo-sac which they inclose. 



In about seven or eight days the ovule is perfectly anatropous ; 

 the inner coat has become much longer than the nucleus, and the 

 outer coat attained a length about equal to the latter. The nu- 

 cleus possesses essentially the same structure as before. 



In this last observation there is a disagreement with Amicus, 

 since he says that the outer layer of the nucleus opens by the 

 separation of its cells, before the coats of the ovule grow over the 

 nucleus. This Von Mohl could not detect; on the contrary, he- 

 perceived the outer cells forming an envelope to the embryo-sac 

 up to the tenth or twelfth day. During this time the embryo- 

 sac has become much enlarged, and its former polyhedral form 

 changed into an ovate. Its cavity is no longer, as before, per- 

 fectly filled with protoplasm, but a space filled with watery fluid 

 has formed in the midst, and the protoplasm principally accu- 

 mulated at the two ends of the embryo-sac, particularly at the 

 upper. The coats have by this time become very much larger 

 in proportion to the nucleus; the inner projects a good way be- 



* Ueber die Entwicklung des Embryo von Orchis Morio. — Botan. Zeit., 

 July 2, 18 17. 



