OF CEYLON AND INDIA. 
445 
to the organism of which it forms a part. We ought rather to 
consider the whole organism or species together, remember- 
ing that there may be for it a kind of general balance sheet 
of profit and loss,* in which it is not necessary even for 
success and expansion that there should be a profit under 
every item, but that the species will lose or gain according 
to the balance on the total of all the items, some of which 
may in themselves be very disadvantageous. In the Podos- 
temaceæ we have a striking case in point. Once in the 
rushing water, the general conditions of life and variation, 
in conjunction with the hereditary peculiarities of the 
family, have produced, so far as we can judge, a certain 
general type of vegetative structure and habit suited to the 
environment, while the floral system has been forced to 
accommodate itself to the changes of the vegetative, the only 
demand made upon it being that it should continue to set 
plenty of seed and try for cross-fertilization as much as 
possible under the circumstances. The disadvantages of the 
floral construction forced upon these plants have apparently 
been made up for by the advantages of the vegetative. 
Another interesting point brought out by this method of 
looking at the facts is the insecurity of the basis on which 
our conceptions of species (at least the large “ Linnean ” 
species), genera, and still more the higher groups rest, 
and the great need for a more exact and quantitative foun- 
dation in our science. Supposing in the case in question 
that the dorsiventrality of the environment and heredity 
were to act only on the vegetative organs, without any 
correlative or induced action upon the floral organs, Ave 
might then have to include almost all the Podostemaceæ in 
perhaps three or four genera at most, as we should only 
have a very few marked distinguishing points, e.g.^ the 
presence or absence of perianth, the distinction betAveen 
shoot- and root-thalli, betAveen thread-like and ribbon-like 
* Cf. Bateson, Materials for the Study of Variation, p. 12 ; MacLeod in 
Bot. Jaarb, V., or abstract in Willis, Manual and Dictionary, vol. I., 
p. 16 . 
