THE CELL 19 
(d) Quite commonly, in plants, adjacent protoplasts 
are joined together by strands of cytoplasm passing 
through minute pores in the cell-wall. 
24. Peculiar Properties of Protoplasm. More is known 
of the structure of protoplasm than is indicated above, 
but a more detailed treatment is reserved until Chapter X. 
Quite as important as the structure of protoplasm are the 
physiological or functional characteristics, or properties, 
that distinguish it from every other known substance. 
The most significant and wonderful of these is its ability 
to reproduce itself. By the vital activities of animals 
and plants, their living substance undergoes a continual 
destruction, which is accompanied by continual construc- 
tion. Parts which are destroyed are constantly replaced, 
and new protoplasm is continually being formed. No 
other known substance can do this. If a crystal, for ex- 
ample, of salt, is suspended in a saturated solution of 
salt in water, some of the salt particles in solution will 
attach themselves to the crystal in a regular manner, so 
as to enlarge it, while preserving its characteristic shape. 
But here, as is readily recognized, the crystal itself is 
entirely inactive. It does not change another kind of 
matter into salt, but merely serves as a center of deposit 
for more salt. Protoplasm, on the other hand, entirely 
alters the nature of the substances which enter into it, 
and recombines them into a substance like itself, with 
entirely new properties in fact converts the non-living 
into the living. 
26. Secretions. In the course of its continual de- 
struction and reconstruction, protoplasm gives off or 
secretes other substances, unlike itself and unlike the 
material of which it was formed; these are called 
