358 Mr Carry, On some points in the structure and [Ap. 30, 



and between the successive groups separation takes place in a 

 corresponding way, the result is of course a series of intercellular 

 spaces continuous with one another and forming a regular canal 

 of very considerable dimensions. The resin-wall of this canal is 

 formed of oblong cells whose longest diameter runs parallel to the 

 long axis of the leaf. These resin- wall cells are specially modified 

 for the purpose of actively secreting or excreting a resiu dissolved 

 in turpentine so as to form a semi-fluid balsam, and this product is 

 poured into and densely fills the cavity of the resin passage which 

 acts as a reservoir for it. The resin secreting cells are easily dis- 

 tinguished by treatment with Tincture of Alcanin (Alkanet) 

 when they alone are deeply stained. My observations afford com- 

 plete confirmation of the accuracy of those of Kreuz 1 as to the 

 mode of derivation of the thickened sclerenchymatous protecting 

 wall surrounding each of the resin-ducts from the primitive mother- 

 cell of the resin-duct, and are opposed to those of Frank 2 who 

 states that when the four daughter-cells have increased by division 

 to eight the parenchymatous cells in the row outside them lose 

 their chlorophyll and become sclerenchymatous. They are also 

 opposed to those of Meyen 3 who states that the cells which occur 

 behind (exterior to) those which at first line the passage, step at a 

 later period into this inner circle and serve to increase the number 

 of cells there. Like Frank and Kreuz I have traced the origin of 

 the ducts each to a single mother-cell in transverse section and I 

 therefore differ from N. Miiller 4 who states that they arise from 

 the separation of four primitive cells. 



C. Medullary. The cells of this tissue remain for the most 

 part thin-walled, they are flattened and columnar with then long 

 axis perpendicular to the periphery of the leaf, except in the case 

 of the outermost layer, in which the cells are short and cubical 

 their long axes being parallel to the periphery. This layer forms a 

 sheath for the fibrovascular bundle, and the walls of the cells are 

 thickened, especially on the side towards the palisade tissue. Tbey 

 are united together without intercellular spaces, and their proto- 

 plasmic contents, with the exception of a parietal layer lining the 

 wall, disappear at a very early period in the leaf's history, leaving 

 a single nucleus of very large size and oval or round form usually 

 lying freely in the cell cavity and not in any way connected with 

 the walls. 



These nuclei when treated with staining re-agents, e.g. Saffranin, 

 Haematoxylin, Osmic acid, or Methyl green, exhibit the character- 



1 "Beitrage zur Entwicklungsgeschichte der Harzgiinge einiger Coniferen." Sitzb. 

 der 1c. Akad. der Wisseiisch. Wien, lxxvi. Oct. 1877. 



2 Beitrage zur Pjianzenpliysiologie, 118 — 123. 



3 Phytomie, p. 191 ; liber Secretiomorgane, p. 18. 



4 Pringsheiru's Jahrbiicher, Vol. v. p. 399. 



