228 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
development of normal flowers, but that this minimum varies greatly 
according to the species. On this point plants may be roughly divided 
into the two classes of sun- and shade-plants. If the illumination falls 
below the minimum for the species, either the size of the whole flower 
or of its parts is greatly diminished, or the formation of flowers is com- 
pletely suspended. The corolla is the part first affected. The attracting 
organs are superfluous when the visits of insects cease, as is the case 
with a low illumination, and the flower becomes dependent on self- 
fertilization. 
Many species have only one kind of flower, which varies in structure 
according to the external conditions, being open and capable of cross- 
pollination when the conditions are favourable, closed and self-pollinated 
when the conditions are unfavourable. In other species two kinds of 
flower are produced, differing only slightly from one another, one open 
and chasmogamous, the other closed and cleistogamous. This leads to 
those cases where the plant possesses cleistogamous flowers of very dif- 
ferent structure from the chasmogamous ; and further to those in which 
cleistogamous flowers only are produced. 
In the formation of zygomorphic flowers, recent observations show 
that light has a decided influence, in addition to gravitation ; the upper 
lip becomes gradually reduced as the result of diminished illumination, 
or even disappears altogether, as in some Labiatee. Natural selection 
appears to play only a secondary part, assisting the direct action of 
external physiological factors. 
Diminished illumination has the further effect of hindering or even 
entirely suppressing the production of flowers in flowering plants. 
Rhythmic Growth.* — Mr. T. Meehan gives illustrations of rhyth- 
mic or interrupted, in contrast to continuous growth, in the case of the 
fruit of a number of species of Citrus, especially in the Tangerine orange 
and in a variety known as the “ navel orange,” in which there is an 
attempt to form another fruit at the apex, usually accompanied by a 
failure to produce seeds. Further instances are afforded by the prolifer- 
ous growth of the flower frequent in many Rosaceae, and in the develop- 
ment of the inflorescence of two species of Composite, Heliopsis Isevis 
and Bidens bipinnata. 
Physiological Function of Anthocyan.f — By experiments with an 
alcoholic solution of leaves of Beta vulgaris var. rubra and var. Rapa, 
Herr L. Kny has determined that anthocyan has the property of hinder- 
ing the decomposition of chlorophyll by light. Further experiments 
also showed that it has, in some cases, the power of converting the 
luminous rays of the sun into heat, and that the elevation of temperature 
in leaves containing anthocyan is less behind a blue than behind an 
orange fluid, and less behind the latter than behind a colourless fluid. 
Influence of Mechanical Traction on Growth. £ — From experi- 
ments made by Herr R. Hegler, chiefly on Cannabis sativa, Dahlia vari- 
abilis , Phaseolus multifiorus , Helianthus annuus, and Tropseolum majus, 
* Proc. Acad. Rat. Sci. Philadelphia, 1893, pp. 292-4, 303-6. 
t Atti Congr. Bot. Intemat., 1892 (9 pp.). See Bot. Centralbl.. lvi. (1893) p. 272. 
X Beitr. z. Biol. d. Pflanzen (Cohn), vi. (1893) pp. 383-432 (4 pis.). 
