ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 405 



It is noteworthy that, in all the plants examined, the conducting 

 cells do not appear to be in connection, by means of protoplasmic 

 threads, either with one another or with adjacent cells, such as the 

 sieve-tubes and bast-parenchyma ; but the author believes that the 

 pits are perforated by very fine threads, which are invisible in con- 

 sequence of being composed of a homogeneous transparent albumen. 



Eussow maintains that the perforations in the pits of cell-walls 

 are cotemporaneous with the formation of the cell-wall. During the 

 last stages of the division of the nucleus, in which the protoplasmic 

 threads are stretched between the daughter-nuclei, already at a dis- 

 tance from one another, the cell-wall has the form of a perforated 

 plate, the threads remaining unbroken, and forming a connection 

 between the daughter-cells. He finds that in some cases the 

 radial walls of the cambium-cells have a single row of primor- 

 dial pits ; before each division these about double in diameter ; the 

 fine perforations of the closing membranes also increase ; the con- 

 necting threads of protoplasm probably split lengthwise, and cellulose 

 is formed between them. Tlie perforations between the tangential 

 and transverse walls are formed in the same way, as also the 

 sieve-like perforations in the transverse and longitudinal walls of 

 sieve-tubes. 



The author finds also a mucilaginous protoplasmic substance 

 in the intercellular spaces of young cortex, which is strongly deve- 

 loped in the motile organ of Mimosa ; and here again a communica- 

 tion is effected by means of threads between this protoplasm and 

 that of the cells. 



Continuity of Protoplasm.* — Since his previous experiments on 

 this subject, W. Gardiner has been chiefly employed in testing and 

 improving his methods, and in adding to the number of plants in 

 which he has been able to demonstrate the existence of a continuity 

 of the protoplasm between adjacent cells. 



In certain endosperm cells, e.g. Bentinckia Conda-panna, where the 

 protoplasmic threads traversing the cell-walls are particularly well 

 developed, it is possible to see the threads perfectly clearly by merely cut- 

 ting sections of the endosperm and mounting them in dilute glycerine. 



The method of swelling with chlor-zinc-iod and staining with 

 picric-Hofifmann-blue is in every way perfectly satisfactory, since but 

 little alteration of the structure occurs, and the staining with the 

 blue is limited to the protoplasm. The sulphuric acid method is 

 in the main unsatisfactory, although it is valuable in the case of 

 thin- walled tissue, where violent swelling must be resorted to ; and 

 it is also valuable as affording most conclusive evidence of a pro- 

 toplasmic continuity in those cases where the protoplasmic processes 

 of pits cling to the pit-closing membrane. The author believes, 

 however, that the results obtained can only be rightly interpreted 

 in the light of the results obtained with chlor-zinc-iod. The 

 possibility of seeing the threads depends on their degree of tenuity, 



* Proc. Koyal Soc, xxxvi. (1884) pp. 182-3; also, Arbeit. Bot. Inst. Wiirz- 

 burg, iii. (1884) pp. 52-87 (English). Cf. this Journal, iii. (1883) pp. 225 and 677. 



