914 



ECOLOGY 



greater part of the thickened endosperm walls of vegetable ivory and 

 of the seeds of the persimmon (fig. 1208) and the date; it is "reserve 



cellulose" that gives the characteristic horny hardness 



to these and to similar seeds. 



Although they rarely if ever accumulate in quantity in 

 seeds, a word may be said as to sugars and similar substances. 

 Sugar (particularly saccharose ') frequently accumulates in 

 quantity in stems (as in sugar 

 cane) and in roots (as in beets), 

 being in solution in the cell sap. 

 Related to sugar is inulin, a car- 

 bohydrate occurring in solution in 

 the roots of composites and of 

 various other plants. When these 

 roots are immersed in alcohol, 

 the inulin is precipitated in solid 

 bodies with concentric stratifica- 

 tion layers, as in starch, and also 

 with lines radiating in all directions 

 from the center, suggesting the 

 trichites that characterize sphero- 

 crystals (fig. 1209). As with 

 starch, the behavior of these bodies 

 in polarized light is that of sphere- 

 crystals, yet some investigators 



FIG. 1209. A 

 root cell of the ele- st '" re g ar d them as amorphous 

 campa.ne(lnulaHe- colloids. 

 leniuni) taken from 

 a specimen pre- 



Fic. 1210. An endo- 

 sperm cell from a seed of 

 the castor bean (Ricmus 

 communis), showing protein 

 grains (/>) made up of amor- 

 phous proteins, crystalline 

 proteins (c), and globular 

 compounds of protein with 

 calcium and magnesium, 

 the globoids (g); highly 



Nitrogenous foods. --Ni- magnified . _ From BARNES 



served in alcohol; tXOgenOUS foods, Such as the (Part 11). 

 note the sphentes p roteins are much legs ablm _ 

 of inulin with their 



growth rings and dant m seeds than are starches and fats, but they are 

 with cracks radiat- universally distributed and of much significance. The 

 ing from the center; ordinary pro to p lasm of the living cells is, of course, 



note also that where . r . ... 



growth begins at the nitrogenous; during seed development it is active, but 

 wall, only half of a jt enters a period of comparative quiescence at ma- 

 sphente is formed; tur j ty aga j n becoming active at germination. Nitrog- 



highly magnined. b i , 



enous substances also develop from vacuoles rich 

 in nitrogenous materials and later hardening into aleurone grains (fig. 

 1210). In the wheat grain, as in grasses generally, most of the endo- 

 sperm cells are packed with starch, but the peripheral layer, often called 



1 The sugar of onion bulbs is dextrose. 



