622 JO URNAL, BOMB A Y NA TUBAL HISTOR Y SOCIETY, Vol. X. 



the source of this calcareous deposit on the leaves of the Plum- 

 bagos. He traces the origin of the white crust to the epidermal cells. 

 But Dr. Wilson points out the error of Professor Vines in words which 

 are well worth reproducing here. They are as follows : — " It may he 

 remarked here that Vines * is misleading in the following statements : — 

 * Similar scales (calcium carbonate) occur also on the leaves and 

 herbaceous stems of various plumbaginaceous plants. . . In 

 these cases no glands like that described (water -gland) are present ; 

 it isj therefore, to be concluded that the epidermal cells themselves excrete 

 the calcium carbonate.' " 



(2) With regard to the Mucilage-glands noticed by Dr. John 

 Wilson in the PiumbagoSj I have this to observe : — Dr. Wilson says 

 that in P. zeylanica the mucilage-glands are of the same size as those 

 in P. rosea and P. capensis^ the largest being 38 mm, in diameter. In 

 the specimens of P. zeylanica examined by Dr. Wilson, he says : — *' A 

 large number were seen clustered in the axil of a young leaf." 

 Dr. Wilson gives a graphic figure in his paper, illustrating the relative 

 sizes of the basal and secretory cells of one of these glands, which he 

 modestly calls " a somewhat small example," but which I think is- 

 sufficient, for all practical purposes, in understanding the primitive 

 structure of the mucilage-glands of the entire order Plmnbaginece 

 hitherto unknown in the literature of British Botany. To come to 

 the description of the first sub-division of the Mucilage-glands,^ viz. : — > 

 (a) the stalked external glands ; they are seen outside the calyx and on 

 the rachis in Plumbago zeylanica. Dr. Wilson says that in P. zeylanica, 

 the entire rachis is thickly studded with active glands, like the calycine 

 ones, but more minute. The second sub-division of the Mucilage- 

 glands includes (&) the internal sessile glands. They occur on the inner 

 face of the sepals and are to be seen in P. zeylanica. " Their basal 

 cells are usually four in number," says Dr. Wilson, " but very often 

 two {P. rosea)." He adds that the bnsal cells "in all cases support 

 numerous very thin-walled secreting cells." The sessile glands, be it 

 noted on the authority of Dr. Wilson, "do not offer any point of materia^ 

 distinction from normal mucilage-glands of the leaves." Such is a 

 brief resume of the observations of Dr. Wilson regarding the glandular 

 appendages of the plant I am describing. I have tried to reproduce 

 here every observation of Dr. Wilson on this very interesting question 

 Lectures ou the Physiology of F'^ants, p. 246, Cambridge. 1886. [ J. W. ] 



