178 



PRINCIPLES OF PLANT-TERATOLOGY. 



prostrate in its growth ; hence in the abnormal Con- 

 volvulus the bilobed form of the foliage-leaves and the 

 prostrate habit of the shoot would seem to be directly 

 correlated ; and this particular form of leaf is probably 

 an ancestral one in the order. 



, G. P. Burns describes an adult and a juvenile form 

 of leaf in Proserpinaca palustris. The entire adult 

 form is produced under good vegetative conditions, 

 the divided juvenile form under adverse ones ; the 

 environment does not appear to have any effect. 



Rejuvenescence of foliage consists of an intercala- 

 tion, into the life-cycle of the adult, of phases and 

 stages of that of the seedling plant. As the foliage of 

 the latter, where it differs from that of the adult, repre- 

 sents an ancestral type ; in the same way, whenever 

 the juvenile foliage appears, normally or abnormally, 

 upon the mature plant, the phenomenon must be inter- 

 preted as of a reversionary nature, and as a break or in- 

 terruption in the progressive evolutionary development. 



BIBLIOGRAPHY. 



Attado. — "Divisione della Nervatura e della Lamina in alcune 

 foglie di Buxus sempervirens L." Bull. Soc. hot. ItaL, 

 1895, pp. 179-181. 



Beissner.— " Knospenvariation." Mitth. Dendrol. Ges., 1895, 

 pp. 43-49. 



Blaeinghem. — Mutations et Traumatismes, p. 97. Paris, 1908. 



Bonnier. — " Sur la presence normale des bractees dans Fin- 

 florescence des Cruciferes." Bull. Soc. hot. Fr., vol. 

 xxix (1882), p. 250. 



Boreas, V.— "Zwillingsblatter." Bot. CentralbL, Bd. lv (1893), 

 p. 363. 



Braun, A. — Das Individuum der Pflanze in seinem Verhaltnisse 



zur Species. Berlin, 1853. 

 " TJeber abnorme Blattbildung von Irina glabra ira 



Vergleich." Verhandl. d. 35. Naturf.-Versamrnl. Bot., 



1861, pp. 195-205. (Laciniation.) 

 "Bemerkungen iiber Doppelblatter." Sitzungsber. 



Ges. naturf. Freunde Berlin, 1871, pp. 6-8. 

 Buchenau, F. — "Doppelspreitige Laubblatter." Ber. deutsch. 



bot. Ges., Bd. vi (1888), pp. 179-186. 



