82 t RECORD OF CURRENT RESEARCHES RELATING TO 



the epidermal cells of Bhododendron ponticum and Draccena Draco. 

 The cells are usually not entirely filled with protoplasm ; roundish 

 lumps or striated Liyers mostly lie near the cell-wall. In the mass 

 lie larger granules, and these form the knots which are connected 

 with one another by nets of fine threads with very narrow round, 

 oval, or angular masses. This reticulate structure of the protoplasm 

 varies in form and distinct-ness. 



The cell-wall also exhibits a filamentous structure ; the reticula- 

 tions appear gradually to pass over into the substance of the cell-wall. 

 Two adjoining cells usually communicate with one another by means 

 of cavities and crevices which are traversed by granules and threads ; 

 so that the cells are thus closely connected together by the uniting 

 threads of protoplasm. The contents of the canals are often to be 

 clearly made out, but are often scarcely to be distinguished from the 

 cell-wall, since they may gradually acquire the same refractive jiower 

 as the cell-wall. Chlorophyll-grains and coloured portions of the 

 reticulations are also found, not only in the cavities of the division- 

 walls, but even in their substance. The cuticle of the cells is also 

 not homogeneous, but exhibits reticulate and granular deposits. The 

 same is also the case with the hypodermal cells ; but among their 

 contents are found also small roundish granules with a reticulate 

 structure. A similar structure was manifested by Aloe arhorescens, 

 Crocus, Hyacinthus, and Mentha. 



The origin of the reticulate from homogeneous protoplasm can 

 be readily followed out in the aleurone grains in swollen seeds of 

 Lupinus FarJceri ; within the same cell the transition takes j)lace 

 from homogeneous aleurone grains to grains with a scarcely per- 

 ceptible, and then to those with an evident reticulation. The 

 behaviour of the threads of the network when starch-grains are 

 being developed can be investigated in the chloroi^hyll-grains of Aloe. 

 In the skeleton of the network lie separate roundish bodies, which 

 are coloured blue by iodine ; while in other chlorophyll-grains the 

 threads of the network are themselves coloured blue by iodine, 

 showing that their substance is gradually transformed into starch. 



Structure of Sieve-tubes.* — Previous investigations of the struc- 

 ture and development of sieve-tubes have been carried out only in the 

 cases of Pinus sylvestris and P. Laricio, which agree in every detail. 

 E. Janczewski has now extended his observations to other ConiferaB, 

 as also to the Gnetacero and Cycadefe. 



The bast of gymnosperms always contains numerous sieve-tubes 

 of uniform shape ; they are jjrismatic, their terminal walls being 

 strongly oblique. The tangential walls of the sieve-tubes are per- 

 fectly smooth, but the radial walls are provided with more or less 

 thick, the terminal walls with especially thick, sieve-plates. These 

 sieve-plates have a roundish form and sharp boundaries, when the 

 cell-wall of the sieve-tube is sufficiently thick and passes suddenly 

 into the sieve-plate, as in Pinus and Abies. When, on the contrary, 



* ' SB. k. Akad. Wiss. Krakau, Matb.-naturw. Sect.,' vii. (1880) p. 29. See 

 ' Bot. Centralbl.,' i. (1880) p. 485. 



