FORMS OF CELLS. 173 
densely interwoven, but also cling together with great tenacity, 
unless they inclose hollow spaces. The tissue (pseudo-paren- 
chyma)’ of sclerotiums, for instance of Secale cornutum, consists 
of remarkably short hyphae, so that upon thin sections it has the 
appearance of parenchyma. It is only upon a longitudinal 
section, softened by a dilute solution of chromic acid (see Micro- 
chemical Reagents), that the threadlike nature of these hyphe is 
likewise clearly brought to view. Notwithstanding their slight 
length, they are very firmly connected with each other. * 
Through subsequent resorption of the transverse walls of a 
more or less elongated row of cells (cell-fusions), long tubes may 
y “aly 
(} OF \V/ Bi </ 
RNA AYA 
) NY Ay V 
V ‘J y 
\} 
Wa i \ oh 
Ai} 4 
N Me ne 
f Ay 
Vii vA any 
Fie, 82.—Hyphe from Fungus Laricis. a, Hyphe; b, longitudinal section through Sg 
the hollow spaces (pores), (Berg.) 
be produced which possess the most varied physiological func- 
tions, sometimes as vessels (in the woody structure), sometimes 
as sieve-tubes (in the phloém), and sometimes as lacticiferous 
ducts (in the fundamental tissue); all being thus designed ir 
conducting purposes. 
Tf the cells lie densely upon each other, they are sfirialy cemented 
together by the intercellular substance* (middle lamella) (Fig. 
64 x); if, on the contrary, they are not in contact with each 
1 Wevsos illusion, 
* Inter, between, and cellula, cell, 
