Excerpt from The Botanical Gazette, Vol. 47: January-June, 1909 (Classic Reprint)
After this work had continued for some months, considerations were given to conditions appearing with some regularity whether Spirogyra was being studied under natural or under artificial environ ment. As a possible constant condition, it was finally decided to give special attention to the subject of periodicity. In this paper only those experiments will be mentioned which seem to have some bear ing on this subject. Although laboratory studies are of minor importance in the subject of periodicity, in the present discussion they will appear first.