227 



especially Sempervivum tectorum ^) and Papaver orientale. 

 The examination of Sempervivum deserves spécial attention 

 by its accuracy and completeness, illustrated moreover by 

 excellent figures. The degrees of transformation from 

 stamen to pistil are the following: broadening of the 

 connective, by which process the thecae become more 

 separated; shrinking and final disappearing of the pollen- 

 cavities; appearance of ovules in the clefts between them ; 

 increased growth of the back of the connective resulting 

 in a bending over towards the pistil, disappearance of 

 the front anthervalves and at last an open carpel with 

 two pariétal placentas. Thèse placentas may grow into 

 one and in this way complète a perfect pistil ^). 



In Papaver almost the same changes were observed, 

 that is to say, that also in the widening clefts there ap- 

 peared ovules and the pollen-cavities receding before the 

 increasing placentas. But whilst in Sempervivum the 

 ovules are born in the gradually deepening clefts, in 

 Papaver the cellular tissue comes forth out of the cleft 

 and brings the ovules to the surface. 



Our Tobacco may in ail respects be compared with 

 Sempervivum and Papaver, for also in Tobacco the placentas 

 arise simultaneously with the disappearance of the four 

 pollen-cavities on both sides of the connective. 



For ail that there remains one noticeable différence, for 

 whereas in the cases described by von Mohl the final outcome 

 is only one carpel, our figures show that, although the inner 



1) Du Petit Thouars seems to hâve been the first to observe the 

 pistillody of the stamens of Sempervivum tectorum, viz. in 1807. 

 Comp. A. P. de C a n d o 1 1 e, Organ. Végét. T. I, p. 546. 



2) Also M a s t e r s gives on p. 351 of his Veg. Teratology (Ger- 

 man transi.) drawings of the pistillody of the stamens of S. iec^orww. 

 Although his figures are inferior to von M o h l's, yet they express 

 the same way of transformation : production of ovules in the latéral 

 clefts, falling off of the loculaments and broadening of the connective. 



