METAMORPHOSIS. 



211 



dissected as in the normal frond (fig. 139). Mr. L. A. 

 Boodle also observed the same phenomenon in a speci- 

 men of A. hirsuta which had been sent to England 

 from Jamaica, and whose leaves had been cut off 

 previously ; the abnormal leaf had sprouted from the 

 dry rhizome after it was planted at Kew. 



In proliferated cones of the horse-tail {Equisetum) it 

 is not uncommon to find transitional forms between 

 the peltate sporophylls and the toothed leaf-sheaths. 

 Such were observed in a cone of E. maximum ; at its 

 base the " collar " had developed as an ordinary leaf- 

 sheath. The abnormal sporophyll, in its least modified 

 stage, had been prolonged on its upper side into a long, 

 tapering scale-leaf structure ; one such structure, whose 

 broad peltate base bore three or four sporangia, had 

 three tapering lacinise at the upper end (PI. XLIX, 

 figs. 10 and 11). In another sporophyll the tapering 

 tip was folded inwards on itself and bore a small 

 sporangium on one of its margins at the base, while 

 the normal large four or five sporangia occurred on 

 the broad, lower peltate part (PI. XLIX, fig. 12). 

 The most modified sporophylls resembled the ordinary 

 leaves, but in such cases there was a deep downward 

 bend towards the dorsal (lower) side, this bent portion 

 representing the peltate part of the normal sporophyll 

 (PI. XLIX," fig. 13). A leaf of this kind is a very 

 interesting transitional structure, for it portrays the 

 unfolding and straightening out of the peltate portion 

 of the leaf, which may conceivably have originated in 

 the past by a double fold (downwards and upwards) 

 of the leaf, combined with abortion of the apex. In 

 the last-mentioned case there has been an elongation 

 both in the stalk (to form the sheath) and in the upper 

 apical part to form the tapering sheath-teeth. In one 

 such sporophyll two sporangia were inserted on the 

 dorsal side of the sheath near its edge (PI. XLIX, 

 figs. 10-13). 



The importance of the above abnormalities in 

 Equisetum lies in the exact homology which is seen 



