tes, induces vegetative growth. This can
be effected by culture in feeble light or in light deprived of the
yellow-red rays: on the other hand, flower-production follows an
increase in light-intensity. These results are essentially in agreement
with well-known observations on cultivated plants, according to which,
the application of much moisture, after a plentiful supply of manure
composed of inorganic salts, hinders the flower-production of many
vegetables, while a decrease in the supply of water and salts favours
flowering.

ii. INFLUENCE OF THE ENVIRONMENT ON THE FORM OF SINGLE ORGANS. (A
considerable number of observations bearing on this question are given
by Goebel in his "Experimentelle Morphologie der Pflanzen", Leipzig,
1908. It is not possible to deal here with the alteration in anatomical
structure; cf. Kuster, "Pathologische Pflanzenanatomie", Jena, 1903.)

If we look closely into the development of a flowering plant, we notice
that in a given species differently formed organs occur in definite
positions. In a potato plant colourless runners are formed from the
base of the main stem which grow underground and produce tubers at their
tips: from a higher level foliage shoots arise nearer the apex. External
appearances suggest that both the place of origin and the form of these
organs were predetermined in the egg-cell or in the tuber. But it was
shown experimentally by the well-known investigator Knight (Knight,
"Selection from the Physiological and Horticultural Papers", London,
1841.) that tubers may be developed on the aerial stem in place of
foliage shoots. These observations were considerably extended by
Vochting. (Vochting, "Ueber die Bildung der Knollen", Cassel, 1887; see
also "Bot. Zeit." 1902, 87.) In one kind of potato, germinating tubers
were induced to form foliage shoots under the influence of a higher
temperature; at a lower temperature they formed tuber-bearing shoots.
Many other examples of the conversion of foliage-shoots into runners and
rhizomes, or vice versa, have been described by Goebel and others. As in
the asexual reproduction of algae quantitative alteration in the amount
of moisture, light, temperature, etc. determines whether this or that
form of shoot is produced. If the primordia of these organs are exposed
to altered conditions of nutrition at a sufficiently early stage a
complete substitution of one organ for another is effected. If the
rudiment has reached a certain stage in