forms as members of so-called “ everlasting ” bouquets. This 
whole colony of Nelumbo, originally planted in a box about four 
feet square, last year escaped from the box. The large area it 
now occupies would seem mute testimony that the Brooklyn 
environment compares favorably with its East Indian home. 
The writer has been particularly interested in the opening and 
closing of the water lilies. What is its cause? What are the 
mechanisms involved? Why do some sorts open at night and 
others in the daytime ? These are problems which in part still 
await solution, and would furnish an interesting topic for investi- 
gation. Conrad,* in his monograph on the water-lily, says, “ We 
must conclude, therefore, that light is . . . the principal stimulus, 
causing in these closure, in other species opening of the flower. 
The difference in effect is paralleled in positive and negative 
heliotropism and positive and negative geotropism.” 
Of course the immediate cause of the opening of the petals is 
the increase in size of the cells on the inner or upper face of the 
petal, thus making the total upper surface greater than the under 
and therefore curving the petal outward from the centre of the 
flower. Conversely the closing of the flower must necessarily be 
due to the increase in size of the cells on the outer or under 
surface of the petals causing it to become greater in extent than 
the inner surface and resulting therefore in a curvature toward 
the centre, or closing of the flower. And accompanying this in- 
crease of cells on one side, there may be a shrinkage of those on 
the other. 
But to what is this variation in the size of the cells due? It is 
evidently the result either of unequal growth of upper and under 
surfaces, in which case the flower may be continually getting 
larger day by day, although perhaps imperceptibly so; or it may 
be caused by daily difference in turgescence of the surface tissues 
on upper and under surfaces, in which case no growth of the 
flower would necessarily occur. 
And as to the cause of these differences in the rate of growth t 
or of turgescence of the cells we come finally to light as the 
stimulating factor, which as Conrad states, operates differently in 
in different species, a phenomenon which has a direct parallel in 
the opposite effect which gravity, for example, has on root and 
shoot of an ordinary plant. Arthur H. Graves. 
♦Conrad. H.S. The Waterlilies. A Monograph of the Genus Nytnphaea. 
Carnegie Inst, of Wash.. Pub. 4. 1905, p. 1Z0. 
t According to a recent authority, growth in plants is essentially the hydra- 
tion of colloids in the cell accompanied by metabolic changes necessary to the 
formation of new living matter, a process to which materials in the cell sap 
contribute. 
The Leaflets are published weekly or biweekly from April to June, and 
October to November, inclusive, by The Brooklyn Botanic Garden, Brooklyn, 
N. Y 
Telephone: 6173 Prospect. Mail address: Brooklyn Botanic Garden, Brooklyn. 
N. Y. 
