414 MORPHOLOGY. 



cells may always be easily observed. Usually one of the new cells fills 

 up the whole vesicle, and the rest are formed in the suspensor. Some- 

 times (?) several cells combine, simultaneously, to fill the germinal 

 vesicle. Meyen himself has given most beautiful evidences of this in his 

 plates, e. g. Physiologic, vol. iii. PI. XIII. fig. 42., the free cytoblasts 

 in the germinal vesicle ; fig. 43. the young cells with their cytoblasts ; 

 fig. 35., in the uppermost cell of the germinal vescicle, two free cells with 

 their cytoblasts; figs. 11. and 14., free cells with cytoblasts in the ger- 

 minal vesicle. Two other peculiar conditions must also be discussed 

 here. Not unfrequently the pollen-tube swells up before its entry into 

 the embryo-sac (in Ceratophyllum, Taxus, Juniperus), and this expan- 

 sion, lying in the parenchyma of the nucleus, or in the micropyle canal, 

 becomes likewise filled with cells, and remains thus perceptible for a long 

 time (in Cynanchum). In other plants, on the contrary, especially in 

 the Naiadacece and Scitaminece, the pollen-tube forms an expansion 

 inside the embryo-sac, which sometimes resembles a somewhat flattened 

 globule (in Potamogeton, Maranta, Statice], sometimes is a longish 

 cylindrical body (in Tropceoluni) : in the first case the pollen-tube then 

 elongates from the summit of the globule ; in the second, from the side of 

 the cylinder, into a prolongation of various length, and then first swells 

 up to form the germinal vesicle. That expansion also in the interior of 

 the embryo-sac, beneath the germinal vesicle, in general becomes filled 

 with cells, and then remains long perceptible. In Tropceolum, by 

 simultaneous absorption of the investing portion of the integuments of 

 the seed-bud, it even comes to lie free in the cavity of the germen, and 

 grows independently, as a cellular cord, quite round the seed-bud, and is 

 indeed distinctly to be recognised on the ripe seed. 



A remarkable aberration from the usual structure of the embryonal 

 globule, as here sketched, occurs in the Coniferee ; but the investigation 

 of these requires so much skill, patience, and perseverance, that I dare 

 not declare myself content with the year's research I have applied to 

 them. What I have observed is as follows ; and I here beg the reader 

 to recall correctly to recollection the description given above of the seed- 

 bud of the Coniferee. The pollen-granules here, of course, arrive imme- 

 diately upon the naked seed-bud, and from the width of the micropyle 

 usually at once upon the papilla of the nucleus. Here they lie for a 

 variable time, then gradually emit tubes which grow through the paren- 

 chyma in various places. Thus they reach the situations where merely the 

 membrane of the embryo- sac covers the enlarged cells of the endosperm, 

 and penetrate into these, quite filling them up. On the commencement 

 of this last process no doubt can prevail in the abundance of examples of 

 almost all our indigenous Coniferee. In Abies excelsa, Taxus baccata, 

 Juniperus sabina, I succeeded in dissecting out the entire pollen-tube 

 from the papilla of the nucleus to the bottom of the little hole, with the 

 expanded portion accurately filling this. During this process, beneath 

 the said enlarged cells (corpuscula, II. Brown) extends downward to the 

 chalaza a gradual solution and absorption of the parenchyma previously 

 formed here, whereby is formed a cylindrical cavity beneath each of those 

 cells, and only separated from it by the epithelium-like layer of cells 

 which surrounds it. Into this cylindrical cavity the pollen-tube now 

 penetrates, breaking through the wall of the little hole ; but I have only 

 twice succeeded, in Taxus and Juniperus, in dissecting out the pollen-tube 

 in unbroken continuity, and here, also, after it had penetrated a little 

 distance into this cylindrical cavity. My further observations -are still 



