ON METAMORPHOSIS IN PLANTS. 121 



inducing the formation of tubers on the aerial portions of 

 the plant, where, in the ordinary course, only leaf buds or 

 flowers would have occurred. He was also able to compel 

 the underground stems (normally tuberous) to develop as 

 leafy shoots above the ground. According to his view, the 

 formation of tubers depends on this, " that a fluid descends 

 from the leaves and stems to form the tuberous roots of this 

 plant". This "fluid" can, however, be compelled to travel 1 

 in the parts above ground, and then the leafy buds become 

 changed to tubers. It seems clear, then, that Knight recog- 

 nised a real metamorphosis as having here taken place. 



Moreover, it is possible to induce, in the same manner, 

 shoots which would ordinarily develop as thorns to grow into 

 leafy shoots. Lothelier'- 2 has lately stated that this may 

 occur in a manner differing from that above indicated. It 

 has already been observed that metamorphosis, regarded 

 from a morphological point of view, consists in this,— that 

 the rudiment of an organ is arrested at a particular period 

 of its growth, and that it thenceforth is changed, as regards 

 its further development. Now, the thorns of Lycium barba- 

 rum> Ulex enropceus, Genista anglica, etc., are merely leafy 

 shoots which have been arrested in their further develop- 

 ment and have undergone sclerosis. If, however, the plants 

 be grown in a very damp atmosphere, the shoots, which 

 otherwise would have formed thorns, continue to grow, 

 according to Lothelier, and elongate into leafy branches. 

 In other words, in the latter case the rudiments of these 

 structures do not remain stationary on reaching a certain 

 stage of development, but continue to grow in a normal 

 fashion, since the external factor which here effected the 



1 I cannot discover whether Knight succeeded in causing the apex of 

 an aerial shoot (which should normally have produced flowers) to penetrate 

 into the ground as a rhizome. I was successful in this during last summer 

 with Ciraea. An account of these experiments, however, will be given 

 more fully elsewhere. 



2 Lothelier, " Influence de l'etat hygrometrique sur les tiges et les feuilles 

 des plantes a piquants " (Theses presentees a la Faculte des Sciences de 

 Paris, 1893). — Whilst repeating these researches, I have not' been able to 

 obtain the results mentioned by Lothelier, at least not in the same measure 

 as he describes. 



