THEORIES OP EMBRYOLOGY. 243 



and that the fovilla is the means of determining the future development 

 of an embryo in it. This utricle is attached to the embryo by a cellular 

 process, or suspensor. Giraud entertains the same opinion, founded 

 on an examination of the ovule of Tropaeolum majus. In this plant 

 he traces the formation of the amniotic or embryo-sac, and primary 

 utricle or germinal vesicle of the embryo, before impregnation, the 

 latter being at first distinct from the sac, but subsequently attached to 

 it by a suspensor ; the fovilla is brought into contact with the outer 

 surface of the embryo-sac, and the first trace of the embryo appears in 

 the formation of a spherical body at the inferior extremity of the pri- 

 mary utricle, this spherical body resulting from a peculiar process of 

 nutrition, determined by the dynamic influence of the fovilla. Giraud 

 also observed a lengthening of the primary utricle and of its suspensor, 

 so as to protrude through the apex of the embryo-sac the nucleus and 

 the foramen, forming cells which partly communicate with the conduct- 

 ing tissue, and partly passed round the ovule within the carpellary 

 cavity. By slight traction of this cellular process, the suspensor with 

 the embryo may be drawn from the embryo-sac through the exos- 

 tome. 



505. Hartig thinks that in some cases, where the pollen-tube 

 cannot be traced directly downwards to the ovule, there is a series 

 of cells which, from their continuity, might be mistaken for it. In 

 some recent observations on Campanula rotundifolia, Wilson appears 

 to think that the pollen- tube is prolonged into the foramen of the 

 ovule. Dickie has noticed, in Xarthecium ossifragum, and Euphrasia 

 officinalis and Odontites, a cellular process proceeding upwards from 

 the ovule into the style, which he thinks may unite with the pollen- 

 tube. Through Dr. Dickie's kindness, I have had an opportunity of 

 seeing these ovule tubes, which appear to end in shut extremities, and 

 not to have a direct communication with the pollen-tubes. These tubes 

 (less than ^ J 55 of an inch in diameter) have been traced by him from 

 the interior of the embryo-sac. They are probably derived from the 

 embryo itself, which, in its early state, may send out tubular prolonga- 

 tions similar to those of the spores of Cryptogamic plants. Tubular 

 prolongations from the ovule were long ago noticed by Mirbel, and of 

 late years by Griffith and Hartig. These authors, however, seem to 

 differ from Dickie, in supposing that the tubes are derived from the 

 embryo-sac, or some of the coverings of the ovule. 



506. Another, or what may be called a third view of impregnation, 

 is, that the pollen-tube does not stop short in the style, but proceeds 

 as far as the foramen of the ovule, enters it, and is applied to the 

 embryo-sac. In the case of the Misletoe, where there are no coverings 

 of the ovule, and consequently no foramen, the pollen reaches the 

 nucleus directly. Meyen, Amici, Mohl, Mulder, and Hofineister, are 

 in favour of this theory. Meyen states, that after the pollen-tube 



