244 



PRINCIPLES OF PLANT-TERATO I.OGY. 



Weisse. — "Ueber Veranderung der Blatfcstellung an aufstre- 

 benden Axillarzweigen." Ber. deutsch. hot. Gres., Bd. 

 xvii (1899), p. 343. 



" Blattstellungstudien an Populus tremula." Fesfcschr. 



f. Ascherson, p. 518. Leipzig, 1904. 



Adventitious Leaves. 



Adventitious leaves, or those which occur on organs, 

 or parts of organs, where they are never normally 

 produced, are very rare, very much more so than are 

 adventitious stems and- roots. 



Groebel excised the growing point of some seedlings 

 of Cyclamen persicum ; this induced the formation of 

 several leaves near the top of the tuberous hypocotyl ; 

 these leaves arose independently at different points on 

 the circumference of the hypocotyl, a truly remarkable 

 phenomenon, being a case of leaf- formation quite apart 

 from the meristem of the stem apex (PL XXII, fig. 3). 



But equally remarkable were the experiments made 

 by Hildebrand on Cyclamen Miliar alcisii and C.creticum. 

 From the stalk of a cotyledon from which the lamina 

 had been removed, sprouted four small stalked leaves 

 in form exactly like the foliage-leaves. When the 

 entire cotyledon was removed the adventitious leaf 

 arose from the epicotyl. 



Adventitious leaves occur on the foliage of Begonia 

 manicata, B. phyllomaniaca, and others in the form of 

 scale-like emergences which may occasionally appear 

 as green leaves. That one leaf should bear another 

 is surely an unheard of phenomenon ! This case may 

 be accounted for as follows : each of these scales may 

 really represent the first-formed leaf of an arrested 

 adventitious bud (these buds, actually occur very fre- 

 quently in B. phyllomaniaca). If we imagine the 

 lateral buds ("bulbils") oi Ly cop odium Selago to 

 become arrested after the formation of the first leaf 

 (which always appears first before there is any sign of 

 the rest of the bud), we should have a comparable 

 example to what may have occurred in the case of 

 these begonias. This explanation may possibly apply 



