66 The Ottawa Naturalist. [Aug. -Sept. 



average time being from 8 to 10 days. A very peculiar feature, 

 but following also on other causes, occurs in squares jtist previous 

 to falling, namely, an outward movement of the bracts (flaring). 

 Sometimes, if abscission does not intervene, the bracts will move 

 inwardly again. This movement is of ver}^ great theoretical 

 interest, since it indicates that there is no lack of turgor (though 

 it does not prove it), and, if this be trtie, an undue loss of water, 

 it is probable, is not a factor. It is evident, from the data which 

 are at hand, that there is some relation between the amount of 

 injury and the time which intervenes between the first insect 

 puncture and the final separation, since, by means of other 

 experiments, I have found that it is possible to cause the 

 abscission of 100 per cent, of young bolls by means of suitable 

 injury (a transverse cut across the ovary), within 48 hours, and 

 90 per cent, have been shed within 24 hours in one series. 

 "Squares" (flower-buds) are not so sensitive, shedding 3 5 to 55 

 per cent, in 36 hours; 40 to 75 per cent, in 48 hours, and the rest 

 later. 



Larger bolls respond only after a longer period, namely, in 

 from 3 to 6 days, or not at all if too large, though they may die 

 without becoming detached. From this we see that a point of 

 development and induration of the tissues of the pedtmcle mav 

 be reached when abscission is not more possible. 



Shedding, of the very young bolls may also Ije caused by 

 cutting oft" the style before pollination, but this, as Fitting found 

 in Geranium and Erodium, depends on the absence of pollination. 

 In E. Manescavi, the petals fall away much sooner after the 

 style was injured than in the uninjured flower. Hannig also 

 found that cutting off the petals, stamens or stigma, from tm- 

 pollinated flowers, and still more readily by removing the ovary, 

 before or after pollination, caused abscission of the whole flower. 

 Wounding of the peduncle did not do so if a portion of the tissue 

 was left, indicating, as I have above shown, that a reduced 

 amount of vascular tissue was able to carry on. the ftmction of 

 the whole. 



Much has been said about the eft'ect of the wounding of 

 leaves by cutting off the blade, and it is generally believed that 

 such injury causes abscission. The results thus obtained are, 

 however, very inconstant and uncertain, as I have found in my 

 own experience. Only a single example. I cut oft" the petiole 

 (in Ampelopsis) from one leaf 10 mm. from the base, and 

 allowed the next lower leaf to remain. The latter separated in 

 24 hours (in a moist chamber), while the stump of the cut petiole 

 remained attached. I have done similar experiments with other 

 species with like restilts, and I have observed injured leaves in 

 nature, finding them to adhere just as long and firmly as un- 



