872 
Journal of Agricultural Research 
Vol. XXIII, No. II 
In connection with the discussion of the literature bearing upon the 
subject which was presented, attention is here called to an article by 
Klebs (jo) on flower formation in Sempervivum, published in 1918, 
which had not become accessible to the writers at the time the previous 
paper was written. Following methods somewhat similar to those 
previously employed by Bonnier, Bailey, Rane, and Corbett, as briefly 
outlined in our former paper, Klebs showed that Sempervivum, which 
normally flowers in June, could be forced into flowering in winter, either 
by means of continuous electric illumination for a few days or by increas¬ 
ing the daily illumination period to more than 12 hours. The Osram 
lamp was used both for continuous illumination and for daily illumina¬ 
tion periods of different duration. This result with Sempervivum is 
essentially the same as that obtained by Bailey and by Rane with spin¬ 
ach (Spinacea oleracea L.)> but Klebs, perhaps, made a more complete 
analysis of the response and his data are more nearly quantitative in 
character. He also studied the effects of change in intensity and quality 
of the light on flowering in Sempervivum. Light seems to be essential 
for the formation of flower primordia. The response of Sempervivum to 
differences in light exposure is interpreted by Klebs as supporting the 
theory previously advanced that flowering is the result of increased 
concentration of the cell sap, particularly with respect to carbohydrates. 
In summarizing, it is stated that in flowering the quantity of the light 
energy is of decisive importance. 
It is especially desirable, also, to call attention here to the remarkable 
life histories of two small marine worms, Convoluta roscoffensis and C. 
paradoxa , as worked out by Keeble (9, p. 31) and others. A curious form 
of symbiosis with a green and a brown alga, respectively, is involved, 
so that these creatures have received the designation “plant animals/' 
The movements of these worms, which live on the seashore, correspond 
with the incoming and outgoing tides. Thus, C. roscoffensis regularly 
sinks below the surface of the sand with the incoming tide and emerges 
as the tide recedes. This synchronism with tidal movement has been 
shown to be due to the alternate exposure to light and darkness as the 
tide recedes and again advances. What is of special interest here, how¬ 
ever, is the remarkable fact that with this organism reproductive activi¬ 
ties occur chiefly at 2-week intervals, beginning with the onset of spring 
tides. This is due to the fact that at this season of the year low water 
occurs only once during the day, the other period coming at night, with 
the result that the worms receive daily only about six hours of sunlight. 
Egg-laying reaches its maximum when the animals are subjected daily to one short 
spell of six hours* light-exposure followed by a long spell of eighteen hours’ dark 
exposure. But—and the fact is remarkable—these conditions of light and darkness 
are precisely those to which C. roscoffensis is exposed during the spring tidal periods 
at which its eggs are laid habitually. 
The observations and conclusions recorded in the former paper con¬ 
cerning the regulatory action of the relative length of day and night on 
flowering and fruiting as against the purely vegetative form of activity 
have been confirmed and considerably extended by further study of the 
subject, as will be outlined in this paper. In view of the marked influence 
of day length on sexual reproduction it seemed likely that plants would 
be found to respond to this influence in other ways, and, accordingly, 
a series of experiments was made to test this possibility. It was found, 
in fact, that the plant is capable of responding in many ways to change 
in the duration of the daylight period. Thus, most if not all outstanding 
