The Histology of the Cell Wall, &c. 437 



IV. " The Micro-organism of Distemper in the Dog, and the Produc- 

 tion of a Distemper Vaccine." By Dr. S. MONCKTON T COPEMAN. 

 Communicated by Sir M. FOSTER, Sec. R.S. 



V. " On the Tempering of Iron hardened by Overstrain." By JAMES 

 Mum. Communicated by Professor EWING, F.E.S. 



" The Histology of the Cell Wall, with special reference to the 

 Mode of Connection of Ceils."* By WALTER GARDINER, M.A., 

 F.R.S., Fellow and Bursar of Clare College, Cambridge, and 

 ARTHUR W. HILL, B.A., Scholar of King t s College, Cambridge. 



PART I. 



" The Distribution and Character of ' Connecting Threads ' in the 

 Tissues of Pinus sylvestris and other Allied Species." By 

 Arthur W. HILL, B.A., Scholar of King's College, Cambridge 

 Received July 17, Read December 6, 1900. 



(Abstract.) 



The research with which this paper is concerned was undertaken 

 with a view of ascertaining to what extent " connecting threads " are 

 distributed throughout the body of any given plant, and for this 

 purpose the endosperm and the various tissues of the hypocotyl, 

 cotyledons, and root of the young seedling of Pinus pinea, and of the 

 adult stem leaf and root of Pinus sylvestris, were examined. 



The results show that the presence of such threads can be readily 

 demonstrated in the case of all cells in which the wall retains its 

 cellulose or mucilaginous character, and that in such young tissue as the 

 growing point of the root all the cells are provided with connecting 

 threads. When the lignified or suberised condition has supervened it 

 is difficult or impossible to identify threads, though even in such cases 

 threads may be recognised in certain of the very young elements. 



In Pinus pinea the tissue of the endosperm, as also that of the 

 germinating seedling, is well connected by threads. 



In the cotyledon the absorptive side next the endosperm (corre- 

 sponding to the lower side of the leaf) shows a certain histological 

 distinction in that the walls of the cells, both of the epidermis and of 

 the subjacent parenchyma, are more richly provided with threads than 

 are the similar tissues of the upper side. No threads, however, occur 



* For the preliminary communication on this subject, see Gardiner: "The 

 Histology of the Cell Wall, with special reference to the Mode of Connection of 

 Cells," ' Roy. Soc. Proc.,' vol. 62, 1897. 



