MONSTROSITIES AND MALFORMATIONS. 255 



due to internal causes, and the question is at least 

 an open one whether many other cases will not 

 also fall into this category. The study of galls 

 has shown that insects can induce the formation 

 of not only very extraordinary outgrowths of 

 tissues and organs already in existence, but even 

 of new formations and of tissue elements not found 

 elsewhere in the plant or even in its allies ; and 

 Solms' investigations on Ustilago Treiihii show 

 that fungi can do the same, and even compel new- 

 tissues, which the stimulating effects of the hyphae 

 have driven the plant to develop, to take part 

 in raising and distributing the spores of the fungus 

 i.e. to assume functions for the benefit of the 

 parasite. Molliard has given instances of mites 

 whose irritating presence in flowers causes them 

 to undergo teratological deformations, and Peyritsch 

 has shown that the presence of mites in flowers 

 induces transformations of petals into sepals, 

 stamens into petals. Similarly De Bary, Molliard, 

 Magnus, Mangin, and Giard have given numerous 

 cases of the transformation of floral organs one 

 into another under the irritating action of funeri. 

 of which the transformation of normally unisexual 

 (female) flowers into hermaphrodite ones, by the 

 production of stamens not otherwise found there, 

 are among the most remarkable. 



These and similar examples suffice to awaken 

 doubts as to whether any teratological change really 

 arises " spontaneously," especially when we learn 

 how slight a mechanical irritation of the growing 

 point may induce changes in the flower ; e.g. Sachs 



