CHAP. VIII. 
FERTILISATION. 
345 
case, to detect the starch, we must employ the aqueous solution 
of iodine, for the alcoholic solution in the first place would 
coagulate the gum, and in the second it colours the starch so 
deeply that, on account of the smallness of the grains, one can 
no longer judge of their colour, and as they are entirely sur- 
rounded with the gum, they may easily be supposed to be 
dark brown. The curvilinear motions of these so called 
pollen animalcules, which are said to have been observed by a 
good many, are very easily explained, since at least many of 
them, being crescent-shaped, when in motion, appear bent to 
the left, the right, or appear straight, according to their posi- 
tion to the eye,” 
With respect to the sexuality of plants, that at least would 
appear, from the facts above recited, to be established beyond 
the reach of controversy ; but lately there has arisen in Ger- 
many a school of Botanists, at the head of which are Schleiden 
and Endlicher, who either deny it, or assert that the nature 
of the phenomenon connected with it has been misunder- 
stood. 
Schleiden states that, ‘‘ if the pollen tubes be followed into 
the ovule, the most delicate process perhaps that occurs in 
botanical investigations, it will be found that usually only one, 
rarely a greater number, penetrates the intercellular passages 
of the nucleus and reaches the embryo-sac, which, being forced 
forwards, is pressed, indented, and becomes the cylindrical bag 
which constitutes the embryo in the first stage of its develope- 
ment, and which consequently consists solely of a cell of pa- 
renchyma supported upon the summit of the axis. This bag 
is therefore formed of a double membrane (except the open 
radicular end), viz. the indented embryo-sac and the mem- 
brane of the pollen tube itself. In Taxus, and especially in 
Orchis, he has been able to withdraw out of the embryo-sac that 
portion of the tube which represents the first stage of the 
embryo, and that indeed at a tolerably advanced period. 
“ The tracing of the pollen tube into the interior of the 
embryo-sac is not so easy in all plants : because the cells of the 
nucleus which are arranged around the summit of the embryo- 
sac are very firm and opake, so that it and the pollen tube 
cannot be exhibited quite free. In these cases, however. 
