NUTRITION 391 
transformed into other compounds. The hemi-celluloses are especially 
common in the endosperm of seeds, and are used as food by the embryo 
in germination. They are deposited in layers on the interior of the cell 
walls, sometimes to the great reduction of the lumen; yet through the 
pits in the thickened walls the protoplast in each chamber maintains 
communication by slender threads with its neighbor. This excessive 
thickening imparts to such seeds a hornlike toughness, as in the coffee 
" bean," or even a bony hardness, as in the date " stones." Sometimes 
cotyledons and even bud scales have like deposits on their cell walls. 
Inulin. Inulin is comparatively restricted, being characteristic of 
a few large families (and occasional elsewhere). It occurs dissolved in 
the cell sap, especially of subterranean organs. It is a very complex 
carbohydrate, though less so than starch, having a formula w(C 6 H 10 O 5 ), 
where n is probably as much as 12 or 18. Whereas starch is built from 
glucose units, inulin is formed by the condensation of fructose units, 
and is comparable in complexity with some of the dextrins, which starch 
yields by digestion. When inulin-containing tissues are put into strong 
alcohol, the inulin is deposited as spherites (see Part III, fig. 1209). 
Fats. Fats are among the most important and valuable of surplus 
foods. In most plants they exist as small drops of oil in the protoplast ; 
but in some cases, as in cacao, they are solid at ordinary temperatures. 
The most universal storage place for fats is the seed, where it is in some 
cases the dominant form of food, and in almost all it is present in greater 
or less quantity. It is by no means confined to seeds, but occurs in the 
flesh of fruits (olive), in rhizomes (potato, iris, and sedges), in bulbs 
(onion), and in roots (carrot). In almost every part of a plant, indeed, 
small quantities of oil may be found, and from many reservoirs it can be 
extracted in commercial quantities. 
True oils must be distinguished from volatile or essential oils, which are common 
in leaves and flower parts. The latter usually have a distinct odor and make a 
temporary translucent spot on writing paper, whereas that made by true oils is 
lasting. 
Accumulated oils are obtained for commercial uses by crushing and pressure; 
but as only a portion of the oil (which forms 2 to 68 per cent of the dry weight) can 
be recovered thus, the " cake " remaining, with its residue of oil and other sub- 
stances, may still be valuable food for animals, as is the case with cotton and flax 
seed. 
Proteins. Proteins, unless they take on a specific solid form, cannot 
readily be distinguished from resting protoplasm. Thus, the " gluten " 
