through Self-adaptation to a Moist or Aquatic Habit. 735 
Monocotyledons are not an ancient group, but that they have branched off 
from the Dicotyledons, or that both groups have sprung from a stock which 
resembled the modern Dicotyledons more closely than it did the Mono¬ 
cotyledons.’ 
Mr. Chrysler, like the other writers quoted, does not appear to see that 
this close connexion is really due to a common cause, viz. degradation 
through an aquatic habit of life. 
13. The Forms and Structure of Aquatic Leaves are the 
Result of the Direct Action of Water. 
In my former paper 1 I suggested that the ‘gashes’ of some Aroids, as 
well as ‘fenestrations’ (e. g. Anadendrum Mouster a, Caladium , Pothos, 
&c.)—recalling those of the lattice-leaved plant ( Ouvirandra fenestralis ), 
such also occasionally occurring in our pond-weeds—were formerly due to 
water, and that they are now hereditary in terrestrial species. 
The pinnate or palmate forms of the leaves of some Aroids and, perhaps 
we may add, Palms, the marginal incisions being quite unlike those of 
a Dicotyledon, may have been acquired in their days of antiquity when 
submerged. 
In support of this contention I can now add that the dissected type of 
foliage when submerged has been proved experimentally to be due to the 
degenerating effect of water upon the protoplasm of the stem. Mr. MacCallum 
succeeded in showing this by setting up osmosis artificially. He dissolved 
certain nutritive salts in the water in which he grew plants of Proserpinaca 
palustris. The result was just what he anticipated, namely, that the super¬ 
fluous water, with which the protoplasm of the stem was saturated, was 
withdrawn, so that the plant was now enabled to bear, and produced subse¬ 
quently fully developed leaves of the aeriform, pinnately nerved, lanceolate 
type. 2 
In the case of Ranunculus heterophyllus the dissected type of leaf has 
been proved, both by Nature and my own experiments, to grow equally 
well in air after being sown in a border, and is thus hereditary, though it 
is a character entirely acquired by the soma. Sowing the seeds of Ranun- 
cidus heterophyllus in a garden border, they all came up and developed 
dissected leaves, but perfectly in adaptation to air. Subsequently the 
floating type appeared, as if the stem had reached to the surface of 
imaginary water, and finally the flowers were borne. This heredity of the 
acquired characters of the foliage lends countenance to the view that the 
pinnate and palmate characters of Aroids and Palms are due to the same 
cause, as well as all their other permanent aquatic types of structure. 
1 loc. cit., p. 522. 
2 Bot. Gaz., xxxiv, p. io6. I have described and figured this more fully in my Heredity of 
Acquired Characters in Plants, pp. 34 ff. (Murray). 
3 c a 
