474 SUMMARY OF CUKUKNT RESEARCHES RELATING TO 



artificially s\vt<lk'U. By dilute sulphuric acid aud a staining reagent, 

 the closing membrane of the pits is shown to possess a different con- 

 stitution from that of other parts of the cell-wall. If more concen- 

 trated acid is used, the staining then shows tliat the dark-coloured 

 protoplasmic tlireads which till up the pit-canals are united by a 

 lighter-coloured slightly refracting connecting piece. A peculiar 

 appearance of "varicosity" presented by some of these connecting 

 threads the author attributes to their assuming occasionally the form 

 of hollow cylinders. A third mode of combination presents the 

 appearance of a direct communication of the protoplasmic bodies 

 through the oj en pits after the resor2)tion of the original sieve-like 

 closing membrane. The protoplasm of the entire epidermis is there- 

 fore not broken uj) by the cell-walls, but forms a connected symplasm. 

 In the long narrow colls t^e nucleus often presents the appearance of 

 a plu^ filling \ip the cavity, while in the broader cells it has retreated 

 to the outer cell-wall. 



For observing the physiological phenomena, sections made by a 

 sharp knife were laid in moist saw-dust in a closed zinc box, and 

 examined after 12 or 15 hours. The result of median sections was 

 that in the 3-5 layers next the wounded surface, layers of protoplasm 

 formed on tlie lateral walls next the cut surface, the nucleus passing 

 over into them; while at a greater distance these " traumatropic " 

 collections of protoplasm were only faintly displayed. A gradually 

 decreasing irritation from cell to cell is therefore conveyed by the 

 exposure of the lateral walls ; this irritation extending uniformly to 

 a distance of about 0-5 mm. The author considers that this irritation 

 cannot be the result of a molecular or micellar vibration of proto- 

 toplasm, as supposed by Niigeli and Strasburger ; but that it results 

 from the continuity of the protoplasm in the epidermal tissue. 



Similar phenomena are presented when transverse and portions of 

 lateral walls are exjiosed by transverse sections at right angles to the 

 median direction, the protoplasm collecting on the transverse walls 

 and the nucleus passing into it, the extent of the irritation being also 

 nearly the same. 



The author thinks that, in normal conditions of the protoplasm, 

 the nucleus is subject to movement in a definite direction independent 

 of the circulation ; and that there is no direct connection between the 

 traumatropic change of position of the nucleus and of the protoplasm. 

 No formation of cork takes place on the wounded surfaces, the healing 

 being effected by the excretion of a hyaline substance related chemi- 

 cally to protoplasm. 



The continuity of protoplasm is more clearly demonstrated in the 

 parenchymatous tissue ; but here the irritation does not result in any 

 change of position of the 2irotoplasm. 



Structure and Division of the Cell-nucleus.* — In continuation 

 of previous observations, M. L. Guiguard finds, even in very early 

 stages, two rows of microsomes in tlie nuclear threads ; and from this 

 he concludes that the segmentation of the microsomes precedes that of 



* Bull. Soc. Bot. Lyon, 1884, 11 pp. See Bot. Cenlralbl., xxi. '1885) p. 76, 

 and this Journfil, ante, p. 262. 



