178 THE CAUSES OF SPECIFIC SHAPE 



occurs not only in related plants, but also between the algae and fungi 

 of many lichens. Since fungal hyphae and the pseudopodia of Myceto- 

 zoa may bore through cell-walls, protoplasmic processes could undoubtedly 

 do the same if endowed with the required solvent or cellulose-softening 

 properties. Even then, however, the two protoplasts would merely come 

 into close contact, and would fuse only when the required affinity existed 

 between them J . Vochting assumes that living continuity is attained in 

 all successful grafts, but this is not certain, although it may be required 

 for permanent union 2 . The harmonious co-operation of the two parts 

 does not support this 'conclusion, for the same is also attained in lichens in 

 which no protoplasmic union of the fungal and algal components appears 

 to take place 3 . Kuhla also states that no protoplasmic connexions exist 

 between Viscum album and its host 4 . 



A secondary formation of fine protoplasmic connecting threads is as readily 

 possible as the fusion in bulk of protoplasts, which in cell-fusions occurs by the 

 solution and removal of portions of the dividing wall 5 . Even if the protoplasmic 

 connexions persist during cell-division and the formation of the partition-wall, 

 a secondary formation is quite possible, and may occur between graft and stock, 

 or between laticiferous tubes and the cells between which they penetrate. The 

 existence of such connexions, either here or in the case of bast-cells elongating 

 between tissue-cells by sliding growth, has not yet been established. Nor are they 

 theoretically essential, for correlation is possible without them. 



Sufficient attention has not been paid to the importance and consequences of 

 the rupture of the protoplasmic connexions, which takes place whenever the cells of a 

 tissue are separated, and hence commonly occurs during the formation of intercellular 

 spaces, for these may appear where pits and protoplasmic threads are present in the 

 walls. A connected question is that as to the existence of extracellular films 

 of protoplasm, which have certainly not as yet been proved to line the intercellular 

 spaces 6 , although extracellular protoplasm is present in ciliated organisms, in 

 Diatoms, and in such Rhizopoda as Gromia oviformis 7 . 



1 Noll (Sitzungsb. d. Niederrhein. Ges. zu Bonn, 14. Juli 1897) only observed a concrescence 

 of the cell-walls in grafted Siphoneae. 



2 Vochting, Transplantation, 1892, p. 1 1 7. The occurrence of hybrids shows that the protoplasts 

 of different species may fuse. 



3 Peirce (Proceed, of the California Acad. of Sciences, 1899, 3rd ser., Vol. I, p. 236) states 

 that the fungi send fine processes into the algal cells, like those which Piptocephalis Freseniana 

 sends into Mucor mucedo. Cf. Brefeld, Bot. Unters. iiber Schimmelpilze, 1872, I, p. 45. 



4 Kuhla, Bot. Ztg., 1900, p. 51. No protoplasmic connexions exist or are necessary between 

 the endosperm and embryo of a seed. 



5 On protoplasmic connexions cf. the summary by Zimmermann, Beihefte z. Botan. Central bl., 

 1893, Bd. in, p. 328. Also A. Meyer, Bot. Ztg., 1896, p. 187 ; Ber. d. Bot. Ges., 1897, p. 166 ; 

 Kohl, Bot. Centralbl., 1897, Bd. LXXII, p. 260 ; Kuhla, 1. c. ; Kohl, Ber. d. Bot. Ges., 1900, p. 364 ; 

 Gardiner, Proceed, of the Royal Soc., 1900, Vol. LXXVII, p. 437. 



6 On extracellular protoplasm cf. Schiitt, Jahrb. f. wiss. Bot., 1899, Bd. xxxill, p. 594 ; Bot. 

 Ztg., 1900, p. 245 ; O. Miiller, Ber. d. Bot. Ges., 1899, p. 423 ; 1900, p. 481 ; Kny, Ber. d. Bot. Ges., 

 1900, p. 43. 



7 Hertwig, Die Zelle u. die Gewebe, 1893, I, p. 26. 



