MORPHOLOGY OF HIGHER PLANTS. i6i 



NON-PROTOPLASMIC CELL-CONTENTS. 



The non-protoplasmic constituents of plants may be said to 

 differ from the protoplasmic cell-contents in two important partic- 

 ulars, namely, structure and function. For convenience in con- 

 sidering them here, they may be grouped as follows : 



(i) Those of definite form including (a) those which are 

 colloidal or crystalloidal, as starch and inulin; (b) those which 

 are crystalline, as the sugars, alkaloids, glucosides, calcium oxal- 

 ate; (c) composite bodies, as aleurone grains, which are made 

 up of a number of different substances. 



(2) Those of more or less indefinite form, including tannin, 

 gums and mucilages, fixed and volatile oils, resins, gum-resins, 

 oleo-resins, balsams, caoutchouc, and also silica and calcium 

 carbonate. 



I. SUBSTANCES DEFINITE IN FORM. 



COLLOIDAL OR CRYSTALLOIDAL. 



Starch is the first visible product of photosynthesis al- 

 though it is probable that simpler intermediate products are first 

 formed. This substance is formed in the chloroplastid (see 

 Frontispiece) and is known as assimilation starch. Starch 

 grains are usually found in the interior of the chloroplastid, but 

 may attain such a size that they burst through the boundary wall 

 of the plastid, which latter in the final stage of the growth of the 

 starch grain forms a crescent-shaped disk attached to one end of 

 the grain (see Frontispiece). Starch is changed into soluble car- 

 bohydrates by the aid of ferments and probably other substances, 

 and in this form is transported to those portions of the plant 

 requiring food. The starch in the medullary rays and in other 

 cells of the wood and bark of plants is distinguished by being in 

 the form of rather small and nearly spherical grains. In rhi- 

 zomes, tubers, bulbs and seeds the grains are, as a rule, quite 

 large, and possess more or less distinct characteristics for the 

 plant in which they are found. Starch of this kind is usually 

 spoken of as reserve starch. 



Occurrence of Starch. — Starch is found in most of the 

 algae and many of the mosses, as well as in the ferns and higher 



