DICHOGAMY. 313 



nalis. Labiates which bear only true hermaphrodite flowers on one plant, and 

 only pseudo-hermaphrodite female flowers on another are protogynous. In the 

 Marjoram {Origanum vulgare), the pistillate (pseudo-hermaphrodite female) flowers 

 are ripe as much as eight days or longer before the true hermaphrodite flowers. 

 The fact must be emphasized that these remarks only refer to such flowers or 

 plants as develop under similar conditions of life, and that they are not applicable 

 to instances where the early or late maturity depends upon whether the habitat 

 is a sunny or shaded one. 



As far as we can tell at present all moncecious plants are protogynous. Sedges, 

 Bulrushes, Bur-Reeds (Carex, Typha, Sparganium), Aroids with monoecious flowers, 

 the Maize (Zea Mays), the monoecious Stinging Nettle {Urtica urens), the Water 

 Milfoil {Myriophyll'wm), the Burnet {Poteriurn), the Bur weed {Xanthium), the 

 monoecious Euphorbiacese {Euphorbia, Ricinus, Buxus), and especially Alders and 

 Birches, Walnuts and Planes, Elms and Oaks, Hazels and Beeches, are all markedly 

 protogynous. In most of these plants, especially the last-named trees and shrubs, 

 the dust-like pollen is not shed from the anthers until the stigmas on the same 

 plant have been matured 2-3 days. Sometimes the interval between the ripening 

 of the sexes is still greater. The majority of dioecious plants also are protogynous. 

 In the luxuriant Willows on the banks of rivers a single species is sometimes 

 represented by thousands of bushes. Some of them bear staminate, the others 

 pistillate flowers. They grow on the same soil, are exposed to the same amount of 

 sunlight, and are fanned by the same breezes, and yet, in spite of identical external 

 conditions, the plants with pistillate flowers certainly precede their staminate 

 neighbours. The stigmas of the Almond Willow {Salix amygdalina) are already 

 mature 2-3 days before a single anther of this species has dehisced anywhere. The 

 same happens in the Purple-willow, Osier, and Crack-willow. This phenomenon 

 can also be observed in the sub-alpine Willows {Salix herhacea, retusa, reticulata), 

 but here the diflference in time is usually restricted to a single day. Among the 

 countless plants of Hemp {Cannabis sativa), which grow up together in the summer 

 in closest proximity from seeds sown on level fields, most of the individuals which 

 bear pistillate flowers have already protruded their stigmas before a single stami- 

 nate flower has opened. The latter do not unfold until 4-5 days after the pistillate 

 plants have begun to blossom, and then only does the wind scatter the pollen from 

 their versatile anthers. In the Dog's Mercury, especially in the perennial species of 

 the genus {Mercuvialis ovata and perennis) which grow in small clumps in the 

 depths of our woods, plants with pistillate and others with staminate flowers being 

 close together on the same soil, the stigmas are capable of fertilization at least two 

 days before the pollen is shed. The same thing is observed in the Hop {Humulus 

 Lupulus), and in many other dioecious plants. 



All these facts are of the greatest importance in the question of the significance 

 of cross-fertilization. If the maturation of the sexes at different times had been 

 observed only in those species of plants which bear hermaphrodite flowers, dicho- 

 gamy might be regarded merely as the completion of the contrivances for preventing 



