CLASSIFICATION OF FARM CROPS 65 



plants. This makes the soil richer in nitrogen and so better 

 for the crop that follows. Nearly all legumes have a strong 

 main root, called a tap root, which grows deep into the ground. 

 When they die the tap roots have a tendency to leave the 

 soil looser than do the roots of plants which are smaller. 



3. Roots. — Certain crops like beets, turnips, carrots, 

 parsnips, and radishes are called root crops. When quite 

 young these plants have a long, slender tap root which gets 

 larger as the plant gets older. It is the enlarged tap roots 

 then which form the root crop. These tap roots, however, 

 do not have nodules on them like the legumes and so do not 

 gather nitrogen. Root crops are used for feed for live stock, 

 and nearly all kinds may also be used for human food. 



4. Tubers. — A tuber is an enlarged underground stem. 

 If we examine a potato plant carefully we shall find that the 

 stem above the ground continues underground as a somewhat 

 smaller white root-like stem. At the end of this root-like stem 

 will be found an enlargement, the potato or tvber. The same 

 examination will show that the real roots start from the base 

 of the above-ground stem and are quite different from the 

 underground stem. Irish potatoes, sweet potatoes and arti- 

 chokes are examples of tubers. 



5. Bulbs. — Doubtless we all know enough about botany 

 to know that a leaf is made up of two parts: the expanded 

 part, or blade, and the stem, or petiole, which connects the 

 blade to the stem of the plant. This petiole is quite easily 

 made out in the leaves of trees, but in such plants as onions 

 and tulips it is not so easily seen. That which we call the 

 onion is nothing but the enlarged and thickened petioles of 

 the onion leaves. The blades of the leaves in the case of the 

 onion are curiously changed. So we say that a bidb is the en- 



