No. 460.) STUDIES ON PLANT CELL.— V. 225 
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 (:01, 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, : 01), or when temperature is sud- 
denly raised (Schrammen, :02). This literature and other 
references are discussed by Koenicke (:01; :04). A flow of 
protoplasm between neighboring cells of hyphz has been 
reported by Reinhardt (92) and Charlotte Ternetz (:00). 
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 hyphze (Smith, : 00). 
There are many forms known, especialy 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 Rhodophycez and the ascocarp 
of the Ascomycetes, both structures apparently sporophytic in 
charater and dependent to a great degree upon the gametophyte 
asa 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. 
