REPRODUCTION OF THE ANGIOSPERMIA. 841 
last few years, existed among physiologists. Thus Schleiden, 
Schacht, and others contended that no germinal vesicle existed 
in the sac until after the contact of the pollen-tube with it in 
the ordinary process of impregnation ; in fact, they believed 
that the germinal vesicle was itself formed from the end of the 
pollen-tube, which, according to their observations, penetrated 
the wall of the sac, and by subsequent development produced 
the embryo. This view was, however, ‘at once combated by 
many accurate observers, who all agreed in describing the 
presence of one or more germinal vesicles or corpuscles in the 
sac before impregnation ; and subsequently, Schleiden himself, 
who originated this view of the origin of the embryo, was con- 
vinced of his error by Raddlkofer, one of his own pupils. 
When the pollen in the process of pollination (page 20) falls 
upon the stigma (jig. 1169, b, a) (the tissue of which at this 
period, as well as that forming the conducting tissue of the style 
and neighbouring parts, secretes a peculiar viscid fluid as de- 
Fig. 1168. Fig. 1169. 
Fig. 1168. A. Pollen-cell of Dipsacus Fullonum. 
B. Po'len-cell of Cucurbita. Each poilen-cell 
is putting out a sing’e pollen-tube. (After 
Thome. )——Fig. 1169. Longitudinal vertical 
section through the uniovular ovary of Poly- 
gonum Convolculus, a. Stigma. b. Pollen-cells. 
ce. Poilen-tube. d. Wall of ovary. gm. Erect 
orthotropous ovule. se. Its embryo-sac. 
ch. Chalaza,—N.B. Two of the polien-tubes 
have penetrated the conducting tissue of the 
style, one of which has entered the micropyle 
ot the ovule, the other not. (After Thome.) 
scribed at page 271), its intine, carrying with it the fovilla, 
protrudes through one or more of the pores or slits of the 
extine (jig. 576) in the form of a delicate tube, which pene- 
trates through the cells of the stigma, by the viscid secretion of 
which it is nourished. In most plants but one pollen-tube is 
emitted by each pollen-cell (jigs. 1168, a and B, and 1169, c), 
but the number varies, and, according to some observers, is 
sometimes twenty or more. The pollen-tube continues to 
