470 KARLING: GROWTH AND REPRODUCTION IN CHARA 
results so far obtained in these experiments are here reported. 
A further, more extensive series of experiments is now being 
made with controlled temperature and light intensities. 
The problem of the periodicities in the life cycles of the algae 
has been widely studied both in the field and under laboratory 
conditions. The literature in this field is extensive, and I shall 
summarize only those results that deal more directly with the 
problem of photoperiodism as related to sexual reproduction. 
Klebs (23) aimed to demonstrate complete environmental con- 
trol over the life cycles of various algae and fungi which he 
studied, but his results have not been generally confirmed. 
Many of his experiments involve environmental conditions 
which are scarcely ever realized in nature and are hardly ap- 
plicable to the explanation of the normal periodicity of algae. 
Similar studies by a large number of investigators both in the 
field and laboratory have yielded diverse results and consequent 
views regarding the underlying causes of algal periodicities. 
The results of these studies, however, cannot be said to have 
been decisive either for the internal or environmental periodicity 
theories. Danforth (13), Copeland (11), Hoyt (22), Williams 
(35), and Transeau (31) hold that the periodic changes in the 
life cycles of the algae that they studied resulted not so much 
from external as from internal conditions and hereditary tend- 
encies. Comére (10), Benecke (7), Fritsch and Rich (16), 
West and West (34), Brown (9), and Hodgetts (21), on the other 
hand, take the opposite view and account for the periodic changes 
on the basis of change in external environment. 
For the higher plants many observers, including Corbett 
(12), Bailey (4), Rane (28), Bonnier (8), and Vochting (32), 
have held that increased illumination led to rapid growth and 
to early production of flowers and seed. Results recently des- 
cribed by Garner and Allard (17), Hendricks and Harvey (20), 
and Adams (1) relating to a wide variety of flowering plants 
show that the relative length of the day is a primary factor in 
growth and development, and particularly in determining the 
occurrence of sexual reproduction. 
Relatively few investigations have been made on the response 
of Characeae to light changes. In 1894, Richter (29), using 
Chara fragilis and C. hispida, found that the shoots were positive 
and the rhizoids negative in their response to light. In cultures 
