No. 460.) STUDIES ON PLANT CELL.—V. 219 
Strasburger (82, p. 246) discussed the permeability of cell 
walls and Gardiner (88) gave a general treatment of the subject 
without, however, any figures to illustrate his conclusions. 
Gardiner discovered for a large number of forms in a wide 
variety of families that the pit membranes were frequently 
pierced by protoplasmic fibrils and that in some cases the fibrils 
traversed the entire thickness of the cell wall. A more detailed 
study with better methods, supplementing his former work and 
accompanied by figures, was published by Gardiner, in 1898, 
this paper forming an important contribution to the subject. 
Gardiner (:00) announced himself strongly in favor of the view 
that the protoplasmic connections between cells were derived 
from spindle fibers of nuclear figures concerned with each cell 
division, a possibility which had been suggested by previous 
writers (Tangl, '79-81; Russow, 83). 
Kienitz-Gerloff ('91) gave an excellent account of the proto- 
plasmic connections in a number of forms, some of them 
pteridophytes, but especially for Viscum album, and followed the 
history of the wall formation, showing that the spindle fibers 
disappeared completely before the development of the connect- 
ing strands of protoplasm. Kuhla (: oo) followed Kienitz- 
Gerloff with more extended studies on the same form, Viscum 
album, tracing the protoplasmic fibrils between the cells in all 
" the chief tissues and establishing the protoplasmic connections 
throughout the individual to an extent that was not known 
before. Hill (:01) described the structure of the sieve-tubes of 
Pinus, dealing especially with the formation of callus and the 
conversion of the connecting threads of protoplasm into strings 
of slime. An excellent review is also given of the work of 
Russow and others, particularly upon sieve-tubes. Kohl (97) 
describes clearly protoplasmic connections between the cells of 
moss leaves. : 
A classification of protoplasmic connections was suggested 
by Kohl (: 00) who distinguished between the solitary state when 
each fibril pierces the cell wall independently of its neighbors 
(Fig. 16, a and b) and a grouped condition when a number of 
fibers arise close together at the bottom of a pit and pierce the 
pit-membrane or middle lamella in a spindle-shaped arrangement, 
