No. 460.] STUDIES ON PLANT CELL V. 225 



4 



ous. It is evident that they bind the whole plant body into a 

 cell complex capable of very delicate interrelations. It is 

 natural that physiologists, Pfeffer and others, should .associate 

 the structures with the phenomena of irritability as the paths 

 over which stimuli may be transmitted from cell to cell and 

 tissue to tissue. Several writers have reported their presence in 

 unusual numbers in irritable structures of plants. The subject 

 is discussed in great detail by Strasburger (:oi, p. 533). 



Besides conducting stimuli, there is much evidence that 

 material may be transferred in solid or semifluid form by the 

 protoplasmic connections from cell to cell and that in some 

 instances there is actually a movement or flow of protoplasm. 

 It is even known that nuclei may pass from cell to cell through 

 pores in the wall, especially after some shock, as in the neigh- 

 borhood of wounds (Miehe, :oi), or when temperature is sud- 

 denly raised (Schrammen, :O2). This literature and other 

 references are discussed by Koenicke (:oi; :O4). A flow of 

 protoplasm between neighboring cells of hyphae has been 

 reported by Reinhardt ('92) and Charlotte Ternetz (:oo). 

 That nuclei may pass through very small space is shown 

 in the development of spores in the Basidiomycetes and in 

 the growth of haustoria from the cells of hyphae (Smith, : oo). 

 There are many forms known, especially among the thallo- 

 phytes, where the communications between cells are so broad 

 as to admit of a very free circulation of their contents. Such 

 conditions are especially well illustrated in tissues around the 

 developing cystocarps of the Rhodophyceae and the ascocarp 

 of the Ascomycetes, both structures apparently sporophytic in 

 charater and dependent to a great degree upon the gametophyte 

 as a host. It is believed that the vitality of protoplasm in sieve 

 tubes, whose nuclei have degenerated and disappeared, is main- 

 tained through protoplasmic connections with neighboring cells 

 and especially the companion cells, when present. Of course 

 where an actual circulation of protoplasm is established between 

 cells or tissues there is made possible a distribution of the 

 products of metabolism in solid form that is very different from 

 the usual diffusion in tissues through cell walls and plasma mem- 

 branes. 



