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 (: oo) 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-'8i ; 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 (:oi) 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 (:oo) who distinguished bet ween the solitary state when 

 each fibril pierces the cell wall independently of its neighbors 

 (Fig. 1 6, 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, 



