PHENOMENA OF HYBRIDISATION IN THE GENUS MENTHA, 181 
IlJ.—Proors or HYBRIDISATION. 
In a general way, the hybrid mints are to be met with in proximity 
to their presumed parents, offering characteristics intermediate between 
those of the parents, and are as a rule sterile. At this point I will 
mention that wherever MW. aquatica and M. arvensis grow in the vicinity 
of each other they have, as it were, an irresistible tendency to become re- 
ciprocally fertilised, thus giving rise to innumerable varieties of MW. sativa 
(together aquatico-arvensis and arvensi-aquatica). On the other hand, 
these are invariably lacking in countries where MW. arvensis exists alone, 
unaccompanied by M. aquatica, and vice versa. This is therefore a 
powerful argument in favour of the double origin of M. sativa, and 
nullifies the opinion of those who look upon this polymorphic hybrid 
either as a verticillata variety of M. aquatica, or as a sativa variety of 
M. arvensis.* 
The same observation applies to the hybrids resulting from the crossing 
of M. rotundifolia and WM. sylvestris, products which I have designated 
under the comprehensive name of sylvestres spurie, by uniting those 
betraying a parentage with I. viridis.t These hybrids, often looked 
upon as legitimate species, are lacking in all the localities where only one 
of their parents exists—for example, in the environs of Paris, where 
M. sylvestris and M. viridis do not exist in a wild state. 
It is, besides, easy to change to a certainty the assumption that we 
deduce from the examination of the facts in Nature. This can be done 
by experimental methods, either analytically, by referring the hybrids to 
their parent species, or synthetically, by reproducing them by a cross- 
fertilisation. I will not here insist on this question of technical 
arrangement, 
IV.—BioLocicaL REMARKS. 
The floral dimorphism of mints has been known for a long time. In 
1848 Bentham wrote in De Candolle’s “ Prodromus”’ (pars xii. p. 165) : 
“ Stamina exserta vel inclusa, flores majores vel minores, sepius sexus diver- 
sitatem nec species diversas indicare jam omnes fere consentiunt.”’ In all 
the species we observe a form submas staminibus exsertis with the stamens 
projecting beyond the corolla, and a swbfemina form where the style only 
is exserted and projects beyond the stamens, which are enclosed in the 
tube of the corolla, and are often abortive; the flower is then smaller in 
all its parts. These peculiarities, biologically interesting, are of no value 
for classification. They are in uniformity with the law of balance, which 
regulates the relative development of the flower and the vegetative 
organs. The exuberance of these latter does damage to the former, and 
is a very frequent cause of sterility, independent of the hybridisations, in 
the genus Mentha. 
V.—DvuRATION OF THE Hyprip Mints. 
Nearly every year, from 1871 to 1885, during the second fortnight of 
the month of August, I repaired to Provins (Seine-et-Marne), where I was 
* See notably Bentham, in DC. Prod. xii. ~ 4 
t See Malinvaud, in Bull. Soc. bot. Fr. xxx. (1883), pp. 477, 478. 
