246 THEORIES OF EMBRYOLOGY. 



tube, in some cases where the embryo-sac is very delicate, pushes it 

 inwards to a certain extent. 



510. Those who object to Schleiden's views, think that he has 

 mistaken the primary utricle, or germinal vesicle, which exists in the 

 embryo-sac before impregnation, for the end of the pollen-tube, and 

 that the cellular filament attaching this to the embryo-sac is totally 

 independent of the pollen-tube. Brown finds that, in the seed of 

 Coniferous plants which have several embryos, there are semicylindrical 

 corpuscles, three to six in number, which are arranged in a circle near 

 the apex. In each of these is a distinct embryonal filament. These 

 filaments frequently ramify, each of the ramifications terminating in an 

 embryo. He believes that these corpuscles are not formed by the 

 pollen-tubes, and that the fact of the ramifications giving rise to rudi- 

 mentary embryos is opposed to Schleiden's views. The corpuscles lie 

 dormant for at least twelve months before being developed. In a 

 female plant belonging to Cycadaceae, another polyembryonous Order 

 of plants, Brown has noted the formation of corpuscles at a time when 

 no male flowers were known to exist in the country. These cor- 

 puscles may probably be considered as analogous to embryo-sacs, or 

 embryonal cavities, such as those in the Misletoe. 



oil. Some of the supporters of Schleiden's views institute a fanciful 

 comparison between the spores of Cryptogamous, and the pollen of 

 Phanerogamous plants. In the former, the cellular germinating body 

 or spore is contained in a case or theca, just as the pollen-grains are 

 in the anther of the latter. In the first instance, the body when dis- 

 charged is at once fit for germination ; hi the second it requires to be 

 transmitted to an ovary, and then to be matured within an ovule, and 

 supplied with a store of nutritious matter, so as to be fitted for inde- 

 pendent existence. These views are theoretical, and do not seem to 

 be borne out by facts. 



512. It will thus be seen that physiologists are much divided in 

 their views relative to this obscure subject ; and when we consider the 

 minuteness of the observations, and the high microscopic powers re- 

 quired, it is not a matter of surprise that there are numerous sources 

 of fallacy. Nearly all agree in the formation of pollen-tubes ; these, 

 according to some, end hi the cellular tissue of the style ; according 

 to others, they reach the ovule ; the influence of the fovilla is com- 

 municated to the ovule either directly or indirectly ; the first cells of 

 the embryo, some maintain, are formed by the end of the pollen-tube 

 directly, while others say indirectly ; and a third party consider them 

 as the result of changes induced by the action of the fovilla. 



513. The opinions which have been recently supported by Amici, 

 Mohl, Karl Mulder, and Hofmeister, are those which seem to rest on 

 the best foundation, viz., that at the tune of the opening of the flower 

 the embryo-sac exists, and that, at its upper or micropyle end, one or 



