300 THE CROSSING OF FLOWERS. 



(Mercurialis), some Docks (Rumex Acetosa, Acetosella), Sea Buckthorn {Hvppo- 

 phae), Poplar (Populus), and the Willows, one of which is figured on last page. 



The fourteenth group consists of species which bear true hermaphrodite flowers 

 on one plant and pseudo-hermaphrodite female flowers on another, and pseudo- 

 hermaphrodite male flowers on a third plant. Caryophyllaceous plants aflbrd 

 many examples of this group, viz. Saponaria ocymoides, Silene acaulis, nutans, 

 Otites and Saxifraga. This arrangement is less often met with in Gentians, as, 

 for example, in Gentiana ciliata. 



A fifteenth group may be added, in which the species have their three kinds 

 of fiowers distributed in four ways on difierent plants, so that they can be divided 

 into four varieties. Spircea Aruncus is typical of this. It produces true her- 

 maphrodite fiowers and pseudo-hermaphrodite male and female flowers. The 

 three kinds of flowers are arranged thus: (1) some plants bear only pseudo- 

 hermaphrodite female flowers, (2) others only pseudo-hermaphrodite male flowers, 

 (3) some bear both hermaphrodite flowers and pseudo-hermaphrodite male flowers, 

 and (4) in addition there are yet other plants whose flowers are all hermaphrodite. 



To complete this summary it should be mentioned that some species exhibit 

 deviations from their usual distribution of the sexes, although this is not often 

 the case. For instance, plants of the dioecious Nettle (Urtica dioica) sometimes 

 occur with both true pistillate and staminate flowers on the same individual. 

 The same thing is occasionally seen in Willows. Most of the plants of the 

 Wild Basil {Glinopodiv/m vulgare) in a given locality bear hermaphrodite flowers, 

 but from a few of the flowers on some plants anthers are either partially or 

 wholly absent. Staminate plants of Vitis cordata were grown in the Vienna 

 Botanical Gardens and only developed staminate flowers for many years, but 

 occasionally true hermaphrodite flowers appeared as well. Single staminate 

 flowers have been repeatedly observed on the pistillate plants of the dioecious 

 Dog's Mercury {Mercurialis annua), and in Lychnis diurna and vespertina true 

 staminate flowers and isolated hermaphrodite flowers are sometimes found to- 

 gether. Single hermaphrodite flowers occur here and there in the inflorescences 

 of the Castor-oil plant (Ricinus communis) among the true pistillate and 

 staminate flowers, and on many plants of Saponaria ocymoides true hermaphro- 

 dite and pseudo-hermaphrodite female flowers have been seen together with 

 pseudo-hermaphrodite male flowers. 



In the light of these results of recent investigation it is evident that the 

 theory expressed in the Linnean System, viz. that the great majority of Phanero- 

 gams bear only hermaphrodite flowers, is not confirmed, and that the view held 

 by Linnaeus as to the completeness and importance of this type of flower breaks 

 down with it. 



But since it is now established that the separation of the sexes in the Vegetable 

 Kingdom is such a widespread phenomenon, it must offer some advantage, and this 

 advantage can only lie in connection with cross-fertilization. By cross-fertilization 

 in Phanerogams we mean here the transference of pollen-cells from one flower to 



