218 IMPORTANT FAMILIES OF PLANTS 



restricted to very limited^ parts of the country. The conditions 

 for success in this line of farming are to be found in very few 

 parts of the country. Old, peat bogs with an ample supply of 

 water are essential. 



CONVOLVULUS FAMILY 



The flowers of this family are perfect and terminal; calyx 

 five-cleft and persistent; corolla, funnel-shaped and five-cleft; 

 stamens five and attached to the corolla. The family contains 

 a large number of ornamental plants of which the morning 

 glory is typical. Many of these plants are so common as to 

 be weed pests. 



Sweet Potato. The most important economic member of 

 this family is the sweet potato (Ipomoea batatas). Some au- 

 thorities claim that this plant is Asiatic, while others claim 

 that it is American. It may possibly be indigenous to both 

 continents. It reaches its greatest development in the tropical 

 countries, where it makes a very luxuriant growth and blooms 

 freely, but it is extensively cultivated in the sandy districts 

 of the temperate zones. Certain varieties are cultivated un- 

 der the name of yams, but the true yam belongs to the family 

 Dioscoreacece. 



Propagation. In the temperate zone, sweet potato plants 

 are grown from roots which are laid in hot-beds, cold-frames 

 or forcing houses, dependent upon the climatic conditions. The 

 plants are then transferred to the field and are most productive 

 in sandy soil. In tropical countries, the crops are usually grown 

 from cuttings set directly in the field. This family includes 

 a number of very troublesome weeds, which are difficult to 

 eradicate except by the use of cowpeas, soy beans or similar 

 smother crops. 



This family also includes the dodder or love vine, which 

 we find growing parasitically on many of our flowering plants. 



