DAILY RHYTHMS IN CERTAIN ROOTS 
381 
growth of leaves of various specjes among which were Secale cereale, Triticum 
vulgare, Allium Cepa, Cucurbita, Melampsora, etc. His results seem to 
show that the time of maximum growth coincides with the time of maximum 
light intensity and that of the minimum growth with the time of minimum 
light intensity. Here, also, a single daily wave of elongation and increase 
in width was found, though its precise relation to the time of environmental 
changes was somewhat different. 
In 1879 Baranetzky (3) published the results of his investigations on a 
number of species including Gesneria tuhifiora, G. cardinalis, Helianthus 
tuherosus (plants from tubers), H. annuus, Brassica rapa, etc. In brief, 
he found that plants which exhibit a regular daily periodicity when exposed 
to the alternation of darkness and light gradually lose this periodicity 
when placed in continuous darkness. The time required for complete 
loss varies from two to three days in the case of Gesneria tuhifiora to 14 
days in that of Helianthus tuherosus. Further, the intensity of the rhythms 
decreases from day to day. Plants grown from the beginning in darkness 
exhibited no periodicity except in the case of the shoots of Brassica rapa, 
some of which showed a very clear and regular rhythm, others a poorly 
defined one, and still others showed none at all. He regards this as due 
to heredity. It could hardly be considered such according to the commonly 
accepted use of the word heredity. A better term would be the " persistence 
of the habit" in the tuber, and its subsequent transference to the shoot. 
In 1892 Godlewski (10) published the results of his researches on the 
growth of epicotyls of Phaseolus multiflorus. In the experiments carried 
out in June 1888, he found that plants growing under normal conditions 
exhibited a single daily wave of elongation, the maximum coming in the 
afternoon and the minimum near midnight. The following year plants 
grown from seeds of the same collecting showed the waves to come some- 
what later, the maximum at evening and the minimum in the morning. 
Further experiments with seeds of a different lot gave two daily waves. 
Plants exposed to uniform conditions showed a very considerable variation. 
In some no marked rhythms were found, and in others rather irregular and 
unsteady ones were found. 
Underground parts. The earliest work on underground parts was that 
of Strehl (36) in 1874, on the radicle of Lupinus alhus L. The conditions of 
his experiments were, however, far from normal, inasmuch as the seedlings 
were grown with their roots in water and kept near a west window where 
they were exposed to moderately strong light. In plants thus subjected to 
the alternation of day and night he found in most cases a single daily wave 
of elongation with maximum coming near midnight and minimum near 
noon. In a few cases two waves were found. 
In 1891 MacMillan (23) reported the results of his experiments upon 
the potato tuber. He found that tubers growing in continuous darkness 
exhibited rhythmic pulsations in their growth, showing two, three, and four 
