917 
of Edinburgh , Session 1885—86. 
vigour of vegetative growth ; while in the well-known expedient of 
root-pruning, nutrition is checked in order to favour sexual repro- 
duction. Again we note the connection between the latter and 
katabolic ascendency, and thus the familiar generalisation that nutri- 
tion varies inversely as reproduction (perhaps most familiarly illus- 
trated in the contrast between the leafy and spore-hearing portions of 
many ferns — Osmunda , Eotrychium, &c.) admits of being more pre- 
cisely restated in the thesis, that as a continued surplus of anabolism 
involves growth, so a relative preponderance of katabolism necessi- 
tates reproduction. 
It is again on the present view readily intelligible why in the 
exceptionally favourable anabolic environment of bacteria and 
many parasitic fungi sexual reproduction should not occur. Mar- 
shall Ward* has pointed out that the more intimate the degree of 
parasitism or saprophytism, the more degenerate the sexual repro- 
duction. The greater the anabolism, in other words, the more 
growth, and the less sexuality. That such comparatively complex 
organisms can continue their asexual reproduction, dispensing al- 
together with the acknowledged stimulus of fertilisation, may 
probably be, at least partially, explained by the presence of abundant 
waste products acting as extrinsic stimuli. 
The relation of sexual to asexual reproduction, which has been 
already referred to in its phylogenetic history (p. 914), is sometimes 
beautifully illustrated in the life of the individual. There are, for 
instance, frequent reversions from the sexual to the asexual process, 
and from the latter to vegetative growth. Among cryptogams the 
sexual reproduction is sometimes suppressed ; thus the fern plant, for 
instance, may spring from the pro thallium asexually. • Nor is it 
uncommon for the asexual reproduction by spores to be replaced by a 
continuous vegetative growth. In the flower-head of an Allium , , 
again, we constantly find that some of the flowers have degenerated 
into asexual buds. A still more beautiful illustration of the condi- 
tions of genesis is afforded by the tiger lily. In this form growth 
at first tends to remain continuous, and the base of the bulb bears 
simple vegetative buds. Further up, however, where nutrition 
reaches its maximum, the axils of the leaves contain buds, which 
are separable though still asexual. Finally, further up still, where 
* “Sexuality of Fungi,” Quart. Jour. Micr. Sci., xxiv. 
