THE TRANSLOCATION OF PROTOPLASM 87 



Kuhla, 1 Kohl, 2 A. W. Hill, 3 Strasburger, 4 and others, it was 

 established that, in the Phanerogamia, Pteridophyta, and 

 Muscineae, living cells are connected with one another by extremely 

 delicate protoplasmic filaments which Strasburger 5 called plasmo- 

 desmae. These filaments traverse the closing membranes of pits 

 in large numbers or pass singly through the more or less 

 thickened unpitted regions of the cell-wall. 6 As was shown by 



1 F. Kuhla, " Die Plasmaverbindungen bei Viscum album," Bot. Ze.it., Jahrg. 

 LVIII, 1900, pp. 29-58. 



2 F. G. Kohl, " Dimorphismus der Plasmaverbindungen," Ber. d. D. bot. Oesell., 

 Bd. XVIII, 1900, pp. 364-372. 



3 A. W. Hill, " The Distribution and Character of ' Connecting Threads ' in the 

 Tissues of Pinus sylvestris and other Allied Species," Proc. Roy. Soc, Vol. LXVII, 1901, 

 pp. 437-439 ; also Phil. Trans. Roy. Soc, Series B, Vol. CXCIV, 1901, pp. 83-125. 



4 E. Strasburger, " t)ber Plasmaverbindungen pnanzlicher Zellen," Jahrb. f. 

 wiss. Bot., Bd. XXXVI, 1901, p. 503. 



5 E. Strasburger, loc. cit., p. 503. 



6 Theodor Hartig (Bot. Ze.it.) discovered sieve-tubes in 1854. Sachs (Flora) in 

 1863 and Hanstein (Die Milchsaftgefasse, Berlin) in 1864 then demonstrated that 

 the cells of sieve -tubes are connected by protoplasmic threads passing through the 

 sieve-plates. One of the more important later papers treating of the details of 

 structure of sieve-tubes and the mode of formation of sieve-plates was that of Hill 

 (" The Histology of the Sieve-tubes of Angiosperms," Annals of Botany, Vol. XXII) 

 published in 1908. 



Tangl (1879-1881) first proved the correctness of suggestions made by Hofmeister, 

 Sachs, and Strasburger that ordinary living cells in a higher plant are intimately 

 connected with one another by demonstrating the existence of plasmodesmae in the 

 ripe endosperm cells of Strychnos, Phoenix, and Areca. Russow found plasmodesmae 

 in the secondary phloem of certain Dicotyledons. Gardiner confirmed Tangl's 

 observations by observing protoplasmic connexions in the endosperm of fifty species 

 of Palms and of many other dicotyledonous and monocotyledonous plants. He also 

 found the connexions in the pulvinus of Mimosa pudica, Robinia pseud-acacia, etc. 

 Kienitz-Gerloff found connexions in a great variety of plants from Liverworts to 

 Phanerogams ; but, as pointed out by Meyer, the worth of his work was unfortunately 

 diminished by a faulty technique. At Meyer's suggestion, Kuhla, as a result of a 

 very careful and laborious investigation, showed that, in Viscum album, the proto- 

 plasm of all the living cells of an individual plant is connected together by bridges 

 into a single symplastic unit. In an interesting schematic diagram of a cross- 

 section of a one-year-old stem of Viscum showing cells of all the tissues from the 

 epidermis to the pith, he gives for every cell-wall the area occupied by pits and the 

 number of plasmodesmae per 100 square [x of wall surface. Kohl investigated the 

 occurrence of solitary plasmodesmae, i.e. those that go through the whole thickness 

 of the cell-wall, and of aggregated plasmodesmae, i.e. those that occur in groups and 

 are confined to the closing membranes of pits, and he found that, usually, the two 

 types of plasmodesmae do not occur in one and the same cell although they may 

 occur in different tissues of the same plant. Hill showed that plasmodesmae are 

 very generally present throughout the tissues of the young seedling of Pinus pinea 



