288 A TEXTBOOK OF GENERAL BOTANY 
Minute seeds. Many plants have minute seeds which are dis- 
seminated by being caught in mud that adheres to the feet or 
other parts of birds or other animals. 
‘Dispersal by explosive mechanisms. Many fruits are so con- 
structed that they explode when ripe and scatter the seeds. This 
method of dispersal is frequently conspicuous in members of the 
bean family, where the 
explosive forces are due 
to stresses arising from 
the drying of the valves of 
the pod. The balsam has 
somewhat fleshy capsules 
which are very turgid. 
W hen these are disturbed 
by contact the segments of 
the pericarps roll up with 
considerable force and in 
such a way that they scat- 
ter the seeds (Fig. 288). 

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sere // 
Dae S 
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Fig. 289. Section showing a few cells of a RESERVE FOOD 
potato tuber 
When a plant manu- 
The cells contain large and conspicuous grains . 
; factures more food than it 
of starch and a small amount of small granules E ; 
of protein. (x 156) needs for immediate use, 
the surplus is stored for 
future use. Food may be stored in certain parts of ordinary stems 
and roots; in especially modified stems, as in the potato and gin- 
ger; in modified roots, as in Sweet potatoes ; or in modified leaves, 
as in the onion. Seeds almost always contain a large amount of 
stored food, which nourishes the young plants until they be- 
come established. Reserve foods are of three general classes: 
carbohydrates, fats and oils, and proteins. 
Carbohydrates. Carbohydrates are organic compounds com- 
posed of carbon, hydrogen, and oxygen, the hydrogen and oxy- 
gen usually being in the same proportion as in water. In 
