46 The Ottawa Naturalist. [June-July 



an armour of spines arranged in clusters, and, as the fruit 

 matures, they are sloughed off. The mechanism involved has 

 not, to my knowledge, been studied. It woidd be useless to 

 speculate on the "biological significance" of this procedure. 



The Abscission of Flowers and Fruits. 



The structure aggregates which, specialized with reference 

 to reproduction, take the form of flower-shoots, and, with the 

 progress of events, of fruit shoots, simple (supporting a single 

 flower) or compound, nia}^ or may not normially be shed.^ The 

 cotton, peach and tomato, under, at present, little understood 

 conditions, sometimes lose a very large proportion of their 

 flowers before anthesis, to the great prejudice, as it is assumed, 

 often not out of harmony with the facts, of the expected crop. 

 Farmers and horticulturists frequently lose 50 per cent, or more 

 of the theoretical returns for the labour expended. 



Abnormal shedding of the entire and perfect flower ivhile 

 open is, for reasons not comprehended, relatively rare, though 

 it is known to occur in cotton, as I have myself observed. 

 Mirahilis jalapa, the well known Four-o-clock, does so phenome- 

 nally imder untoward conditions, and has been studied 

 particularly by Hannig (12), who furnishes in his paper a list 

 of some twenty or thirty other species which may behave 

 similarly. On the other hand, normal abscission intervenes, to 

 remove staniinate flowers after pollination has occurred, in the 

 cucurbits, and before, and as a conditio sine ^ua non to it,, in the 

 hydrocharids. The eel-grass is a classic example, whose stamin- 

 ate flowers are loosened in the morning (Wylie, 13) and, floating 

 on the surface of the water, open and bring their pollen by the 

 chance of currents and surface tension into contact with the 

 stigmas of the pistillate flowers. A still m.ore remarkable 

 behavioiu" is that of the closely related Enalus acoroides, of the 

 eastern tropical shores. This has been more fulh^ studied by 

 Nils Svedelius (14), who points out, however, that Zollinger was 

 the first to record the floating of the staminate flowers. These, 

 according to Svedelius, are released at low tide. Having come 

 into contact with the pistillate flowers, which reach to the surface 

 only at this time, they are grasped by the petals, and in spite of 

 the rise of the tide, are held firmly, and pollination proceeds 

 below the water surface. 



. Just as abscission occurs before and during anthesis, con- 

 ditions may be such as to induce the shedding of the developing 

 fruit. The "boll-shedding" of the cotton intervenes chieflv 

 during the earlier stages of development of the fruit or "boll," 



^With various form of dehiscence this paper has nothing to do. 



