EFFECT OF PARASITIC FUNGI ON THE FORM OF HOST-PLANT. 27 



The two first cases have already been considered. The arrest 

 of the flowers of anemone, as a result of Aecidium puTwtatum, 

 is a further example of Case 2, and at the same time exemplifies 

 Case 4, in that the floral leaves become green foliage leaves, 

 though of a very stunted kind. The petals of Cruciferae hyper- 

 trophied under the influence of Cystopus candidus often become 

 green, and at the same time much altered in shape. 



A particularly interesting case is presented by the develop- 

 ment of the stamens of the pistillate flowers of Lychnis dioica 

 infested by the mycelium of Ustilago violacea. These stamens 

 normally remain rudimentary, but in the diseased abnormal 

 flowers become fully developed like those of the staminate 

 flowers, except that the spores of the parasite replace the 

 pollen in the anthers. Giard^ has designated this phenomenon 

 as " castration parasitaire," and he distinguishes three modifica- 

 tions amongst unisexual flowers. 



(a) Stamens appear in pistillate flowers ("androgene castration 

 parasitaire "). This occurs, as already mentioned, in pistillate 

 flowers of Lychnis dioica frequented by Ustilago. 



(b) Ovaries are developed in staminate flowers (" castration 

 thelygen "). Examples : Carex praecox with Ustilago caricis, 

 Btuihlo'e dactyloides with Tilletia luchloeana, and Andropogon 

 provincialis with Ustilago andrqpogonis. 



(c) In flowers of either sex the sexual organs of the other 

 appear in consequence of the influence of the parasite (" amphigene 

 castration parasitaire "). Giard compares these cases with that 

 of the development of the organs of the latent sex in animals, 

 e.g. of cock's feathers on an old ben, or growth of horns on 

 castrated or "gimmer" animals. In both cases the phenomenon 

 is due to the same cause; in the animals the organs of the 

 latent sex appear as the result of the normal organs becoming 

 functionless or being destroyed by castration; in the plants 

 through stimulation of the latent rudiments by the fungus, 

 which does not, however, cause suppression of the organs 

 already present. In some respects the phenomenon is comparable 

 with what happens when the terminal shoot of a tree is lost 

 and some neighbouring lateral shoot turns vertically upward 

 to replace it. 



The effect of fungi on the reproductive organs of plants 

 ' Mangin and Giard, Bulletin scient. de la France et de la Belgique, 1884. 



