SIGNIFICANCE OF DICHOGAMY. 315 



in consequence of the dichogamy of these Willows. This obviously applies to all 

 other Willows, and generally to all dioecious plants whose flowers are incompletely 

 protogynous. 



In order to show that the same processes obtain in monoecious plants, I would 

 ask the reader to accompany me to the edge of a moor where numerous monoecious 

 Sedges {Gar ex) form the chief constituents of the vegetation. Widely different 

 species grow in varied profusion side by side. Here at the margin of a dark pool 

 Garex acutiformis, Jiliformis, riparia, vesicaria, paniculata, there, on the marshy 

 stretch close by, Garex flava, canescens, glauca, Hornschuchiana, and many others. 

 These Sedges do not all blossom at the same time; one ceases to flower just when 

 another is in its prime, and when, in a third sort, the flowers have just begun to 

 fade. All monoecious Sedges are protogynous. The stigmas have been ripe 2-3 days, 

 and have protruded far beyond their subtending bracts, so that it would seem 

 natural that the pollen, wafted by the wind, would remain attached to them. But 

 the anthers of the staminate flowers of the same species have not yet opened. It 

 is evident then that the stigmas must be pollinated during the first and second day 

 with pollen from other species which blossom earlier, for since the anthers of these 

 earlier species are already open, each gust of wind will shake out their pollen and 

 blow it over the moor, pollinating everything which is capable of being pollinated. 

 The pollen of the same plants (afterwards shed from the staminate flowers above 

 and close to the mature stigmas) can only be received in the second place on account 

 of its later arrival. Thus, we see that incomplete dichogamy promotes hybrid- 

 ization in the first place, and then, only later, a legitimate cross-fertilization in 

 plants with monoecious flowers. 



It is well known that all the plants of a species growing under similar external 

 conditions do not blossom on the same day, and this fact is worth noticing in so far 

 as it might be thought possible for the earlier plants of a species to provide pollen 

 for the stigmas of later plants. This is certainly often the case, but it is also certain 

 that the stigmas of the very earliest plant of a protogynous species can only be, and 

 actually are, fertilized with pollen from another species which flowers still earlier; 

 thus the conclusion already arrived at must remain unaltered. 



It may be taken for granted, since plants with pseudo-hermaphrodite flowers 

 behave exactly like dioecious and monoecious flowers in the manner of the transfer 

 of their pollen, that their dichogamy has the same significance. The spikes of Docks 

 belonging to the group Lapathum, viz. RuTuex alpinus, nemorosus, and obtusifolius, 

 bear principally pseudo-hermaphrodite flowers, which are some of them male, some 

 female, and besides these a few true hermaphrodite flowers. In any one plant, the 

 development of the stigmas is always considerably in advance of that of the anthers. 

 The stigmas are ripe whilst the anthers are still closed. Under these circumstances 

 the first flowers of a plant, whether pseudo- or truly hermaphrodite, can only receive 

 pollen from other plants which have been in bloom for several days, and whose 

 dehisced versatile anthers have been robbed of their pollen by the wind. It may 

 further be taken for granted that any hundred plants of Rumex ohtusifdius, 



