ETIOLOGY OF MALFORMATIONS 193 



way. But organs which arc normally arrested may be caused to develop 

 further by the attack of a fungus. Lychnis vespertina 1 is a common 

 dioecious plant, but it sometimes occurs with apparently hermaphrodite 

 flowers. In all cases which have been carefully investigated this latter 

 condition is the result of an attack upon the female flower by Ustilago 

 antherarum bringing about the full development of the primordia of the 

 stamens which would otherwise be arrested at an early stage ; in the 

 anthers however the spores of Ustilago are found instead of pollen-grains, 

 and the female sexual apparatus is in great part aborted. 



An example of the new formation of organs at places on which they 

 would not otherwise appear is known. We have such in the ' witches' 

 brooms ' which are formed upon the leaves of Pteris quadriaurita in con- 

 sequence of the attack of the fungus Taphrina Laurencia 2 . These are 

 adventitious shoots with malformed leaves, although normal adventitious 

 shoots never appear upon the leaves of this plant ; but in other species 

 the appearance of leaf-born shoots serving the purpose of vegetative pro- 

 pagation is normal. The leaves of these adventitious shoots differ in 

 form and structure from the ordinary leaves of Pteris ; the form may 

 be seen in Fig. 108 ; as to the structure, I need only say that it is much 

 more simple than that of the normal leaves, the leaf-tissue is but slightly 

 differentiated, the epidermis possesses no stomata, and the leaves, teleo- 

 logically considered, are evidently destined here, as they are in the tissue- 

 growths of other ' fungus-galls,' to draw from the plant-body plastic 

 material which the fungus then converts to the formation of its own 

 spores. These deformed leaves are nevertheless merely transformations 

 or arrestments of ordinary primordia of leaves, as is shown in the fact 

 that they are laid down and grow like normal leaves, and that there may 

 appear, seldom it is true, amongst them a normal leaf of Pteris ; this 

 comes about because the fungus-hypha has not pierced the primordium 

 of the leaf. The process is then evidently this in consequence of the 

 attack of the parasitic fungus the leaf-tissue is caused to form an adven- 

 titious shoot which otherwise would not develop here, and the fungus 

 changes by its attack the primordium of the leaf. The first effect 

 recalls at once the formation of galls on Selaginella pentagona, about 

 which we shall say something presently 3 . 



Buchenau 4 found in plants of Luzula flavescens and Luzula Forsteri 

 which were attacked by a brand fungus that the flowers were replaced 



1 Mngnin, Recherches sur le polymorphisme floral, la sexualite et Thermaphroditisme parasitaire 

 tin Lychnis vespertina. Lyon, 1889. For analogous cases in other plants, see Magnin et Giard in 

 Bull, scientif. de la France et de la Belgique, xx (1889), p. 150. 



2 See Giesenhagen, Uber Hexenbesen an tropischen Farnen, in Flora, Erg.-Bd. 1892, p. 130. 



3 See page 197. With regard to the fungus-galls of Aspidium nristatum, ?ee Giesenhagen 1. c. 



4 Buchenau, in Abhandl. d. naturw. Vereins zn Bremen, ii. 

 C.OEBEL O 



