MACFARLANE: SYNCHRONISM IN PLANT STRUCTURES 319 



26, and in wonderfully exact and graded succession, with definite time 

 interval between each, later flowers open along the elongating axis. 

 But just three days before, or on June 23, the central flowers of the 

 cymes on our common Indian bean {Caialpa bignonioides) expand, and 

 for about 16 days thereafter successive blooms open in exact ratio, if 

 weather conditions are favorable. But a decided retardation may 

 occur, if cold winds and wetting rains interfere. 



We would draw attention now to some cases of synchrony in floral 

 parts. From the time of Linnaeus onward descriptions of floral clocks 

 have been frequent, and no matter what value we attach to such, the 

 very device points to a surprisingly exact time during the twenty-four 

 hours when the blooms of each species open. But the maturation and 

 opening of each flower, as well as the behavior of such parts as the 

 stamens and styles of it, may vary according to the degree of thermic 

 energy, or lumic energy, or both that act on these. Such variation 

 seems to explain apparently contradictory results that have been 

 recorded by different botanists. Thus Kerner's attractive state- 

 ments^ regarding Silene nutans and its successive maturation of one 

 row of stamens in each flower, on one evening, of a second row on a 

 succeeding evening, and of the styles on the third, have called forth 

 adverse comment along with the statement that no such exact suc- 

 cession occurs. But first about twelve years ago along the Trafoi 

 Ravine in the Tirol, and nearly seven years ago by Morgarten Field 

 in Switzerland, the writer was able to prove that both statements 

 might apply according to environal conditions. For when the days 

 and nights in August are warm, with clear sky overhead, the exact 

 succession noted by Kerner can readily be traced. But if the days, 

 and even more the nights, be cold, raw and at times accompanied by 

 rains, then a nearly simultaneous maturation of all ten stamens and 

 at times even of the styles may occur. 



By careful observation, however, during warm dry days we were 

 able to determine an even more exact and synchronous behavior of the 

 ten stamens than that noted above. For on the first evening from 

 about 6 to 7.30 the anthers of the earlier 5 stamens matured in circular 

 succession with a clear time interval between each, and then were ready 

 to scatter pollen ; while on the succeeding evening, the second five 

 ripened similarly. Such again calls to mind the time period shown in 

 maturation of the five anthers on the stamens of the giant cow parsnip 

 {Heracleum lanatiim). It was found even that the dropping of the 

 anthers in Silene mentioned by Kerner takes place not together, or 

 irregularly, but in correlated succession if environal stimuli are favor- 



5 Nat. Hist, of PL 2, p. 154. 

 22 



