1890.] Botany. i 367 
should have its name, and that English writers on the subject should be 
freed from the necessity of expressing themselves upon it in paraphra- 
ses. Unless some better term has been devised or some little-used 
term should have priority, it is proposed to term the motion of twining 
plants—so far as that motion is the result of the specific irritability— 
dromotropism, and we can then speak of such twining shoots as dromo- 
tropic. 
Again, certain very well-known but as yet very poorly understood 
movements take place during fertilization and conjugation, by means 
of which antherozoids are directed to the waiting oösphere,—perhaps 
passing down the long neck of an archegonium ; by which pollen tubes 
reach the oösphere in the embryo-sac of phanerogamous plants, and in 
view of which it is possible for the conjugating, motile or resting, . 
sexual cells of zygophytic plants to come in contact with each other 
through an intervening space of air or water or soil. In the case of 
the higher cryptogamous plants, where clear differentiation of male and 
female organs and cells exists, the directive impulse seems to originate 
in the odsphere itself. Possibly the movement of the antherozoids 
towards the odsphere—a movement of such great biological importance 
—should be explained by attributing, as has been done, to the 
odsphere the power of excreting some chemical compounds which, 
while of the nature of waste products or excreta, nevertheless exert a 
stimulative and directive effect upon antherozoids in the near vicinity. 
So far as I can learn carefu! experiments to indicate just how far the 
odsphere can exert this stimulative influence have not yet been made. 
It would be of the greatest importance to discover through how many 
millimetres of water, for example, a polypodium antherozoid would 
find its way to the proper archegonium, but in the present state of the 
knowledge upon this topic, we cannot speak very accurately. Should 
the conjecture of a chemical stimulus be the correct one, the whole 
series of phenomena connected wita conjugation and fertilization, to 
which passing allusion has been made, would possibly be most analogous 
to the hydrotropic curvatures of roots and shoots in view of which 
growth takes place from a region less saturated with moisture to one 
more saturated, or vice versa. For evidently if any aromatic excretum 
is given off from a sexual cell it would be in greater quantity the nearer 
one came to the originating cell. 
Movements, then, of antherozoids and pollen-tubes, since they are 
clearly irritable movements, might appropriately be termed gonotropic, 
and the movements of the water cells themselves towards the female 
might be termed gonotropism. If it were deemed necessary to dis- 
