184 THE VEGETABLE WORLD. 
germ within the grain of pollen, and that it is formed of the end 
of the pollen-tube itself, while this extremity is lodged in the 
embryonic sac, whence it is driven back before it. 
This theory, which reproduced, and seemed to take for granted, 
in the vegetable kingdom the celebrated hypothesis on the e- 
closure of germs put forth by Buffon for the animal kingdom, 
made much noise among the learned in Europe. It was supported 
by the personal observations of many of our best botanists; but it 
could not long resist the multiplied investigations that the im- 
portance of the subject called forth on all sides. : 
M. Amici, Mohl, Uuger, and Hoffmeister soon demonstrated 
_ that, in fact, when the pollen tube had once reached the embryo- 
sac, it remained there, attached by its external wall, and that there 
its functions ended with its life; whilst a little vesicle plunged 
in the mucilaginous juice with which the embryo-sac is filled, 
absorbs by endosmose the fertilising elements which the pollen- 
tube has doubtless passed through its constituting membrane, 
and that this element is then developed so as to form the 
embryo. 
Schleiden’s theory of the pre-existence of vegetable germs 
received its final blow, when, in 1849, M. Tulasne, one of the ablest 
of French anatomists, published his magnificent studies on vege 
table embryogeny. M. Tulasne had always observed that the obtuse 
extremity of the pollen-tube was brought close to the membrane 
of the sac, strongly adhering there without causing any Pe! 
ceptible depression. At some distance from the point of contact, 
there was developed, on the membrane of the sac, a vesicle with a 
circular base, at first like a blister, which by cellular growth was 
soon transformed into the embryo. Fig. 280 represents the result 
of M. Tulasne’s observations, and the manner in which the 
extremity of the pollen-tube is introduced into the nucleus. F 18 
282 is an internal section of the same organ, showing the formation 
of the vesicle about to become the embryo, and Fig. 281 shows 
this vesicle now become a small globe of parenchymatous tissue, ® 
sort of rough sketch of the embryo, The embryo thus formed may 
acquire considerable development, and absorb for its own use all 
the soft matter contained in the embryo-sac ; or it may be limited 
in size, and this soft matter, becoming a permanent and cellular 
