of Vegetable Embryology. 233 



Schleiden takes for the extremity of the pollen tube. Again, 

 if the membranous sac or primary utricle of Mirbel be only 

 the extremity of the pollen tube, it would occur that, during 

 the first formation of that utricle, the posterior part of the 

 tube would show itself externally to the nucleus ; but Mirbel 

 has shown that the utricle originates in the cavity of the nu- 

 cleus, and for a long time is wholly lodged there, giving no 

 indications externally of its presence. A fact which appears 

 to strike at the very foundation of Schleiden's statements is, 

 that at the period when the observations of MM. Mirbel and 

 Spach were made, impregnation could not possibly have taken 

 place, for the female organs of the Zea were entirely covered 

 by from seven to ten broad bracteae, all closely infolded within 

 each other ; so that under this disposition of parts it was im- 

 possible that the pollen tubes could arrive at their destination. 



3rd. Schleiden states that the part of the pollen tube lodged 

 in the caecum of the embryo-sac becomes club-shaped, and in 

 its cavity is produced a mass of utricular tissue, with which it 

 becomes filled ; whilst the posterior part of the tube still con- 

 tinues in its original membranous condition ; that portion 

 soon disappears, while the extremity of the tube becomes 

 transformed into the embryo, and commences a new develop- 

 ment. Now M. Mirbel has shown that the first appearance 

 of the primary utricle precedes the application of the pollen ; 

 that it is independently engendered in the ovule ; and that, 

 conjointly with the utricles which it produces, it commences 

 the formation of the embryo. The same observer has moreover 

 stated that the flaccid membranous tube by which the 

 young radicle terminates, is not the posterior part of the pol- 

 len tube, but the suspensor, or appendage of the primary 

 utricle, of which it evidently forms a part, as its elongation 

 takes place from within outwards, and not from without in- 

 wards. 



The refutation of the doctrines of the German phytologists, 

 thus apparently afforded by the observations of MM. Mirbel 

 and Spach, would serve to establish the generally received 

 opinions regarding the sexual functions of the reproductive 

 organs of flowering plants, and to maintain the present views 



