QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE, 305 



there appears to be no reason for accepting with Sanio the 

 existence of a terminal cell to the plerome segmented after 

 the fashion of the terminal cell in Cryptogams. 



In many cases the essential distinction between periblem 

 and plerome cannot be recognised. The external layers of 

 periblem give origin, in all cases, to the phylloraes. According 

 to Hanstein, they originate in the second, third, and fourth 

 layers, butWarming considers that it is only exceptionally that 

 the first layer docs not also take part, especially in the case 

 of floral leaves, and that in some cases this is the only one 

 that is active. The dermatogen also plays an essential part 

 in the formation of leaves, especially the floral ; in many 

 cases the bracts, stipules, and bud-scales consist principally of 

 epidermis. 



Hofmeister appears to have been wrong in supposing that 

 buds are always formed on the summit of the stem. Usually 

 vegetative buds envelope after their subtending leaf; in 

 ^sculus, Syringa, etc., it is easy to show that there are 1-4 

 pairs of leaves above those of the axils, of which the first 

 segmentations for the formation of a bud have taken place. 

 In the case of inflorescences the highest new structure de- 

 veloped from the stem is frequently a bud, which may arise 

 before, simultaneously with, or after its subtending leaf, or 

 without there ever being even a trace of this as mCruciferce and 

 Compositce. The question then arises whether these buds — 

 originating, as they do, on the summit of the stem — are to 

 be considered as formed by a partition of the punciwn vege- 

 tationis. Generally speaking, however, especially when the 

 apex of the stem is very conical, it is easy to make out that 

 the buds which originate at the base of the cone are below the 

 group of apical cells, forming the true punctum vegetationis 

 (as in Compositce) . In a small number of cases buds originate 

 so near the actual summit of the stem that the peripheral 

 cells of the punctum vegetationis actually do take part in their 

 formation. 



In some such cases there is a true dichotomy of the 

 vegetative point ; its cells divide into two or more groups, and 

 each of these becomes a point of departure for a new forma- 

 tion of buds. This has been ascertained in Hydrocharis and 

 ValUsneria, in the ramification of the tendrils and less dis- 

 tinctly of the principal axis of Vitis vulpiua, in the inflores- 

 cences of Aslepiadacece, in the scorpioid cymes of Hyoscyamus 

 and Borraginacea, and in some other cases. 



Ramification by partition of the punctum vegetationis and 

 by the formation of lateral branches have been regarded as 

 very diflerent modes. Warming considers them as not 



