Further Growth and Duration of Plants 27 



plants take two years to bear their fruit. The first year is 

 spent in making food, part of which is stored, usually under 

 ground. The second year a flowering shoot is sent up and the 

 food is used to ripen the seed. These are Biennials. In 

 cold countries, or where it is very hot and dry, work has to 

 stop for part of the year ; but in a mild climate the work of bi- 

 ennials may continue without interruption, and so the seeds 

 ripen in less than two years. Many are found in vegetable 

 gardens. Members of the carrot family are frequently biennials, 

 though some plants of this family continue their growth under 

 ground year after year, the part above ground dying down each 

 year. This is also the habit of many Pelargoniums (" Gerani- 

 ums "). If plants or their parts live more than two years they 

 are called Perennials. 



The underground part which stores food is sometimes a 

 stem, sometimes a root. " April Fool " {Hcemanthus) stores 

 food in a large bulb. A bulb is a short thick stem, surrounded 

 by the fleshy bases of foliage leaves. Gladiolus^ Morcea, and 

 their family, the Iridaceae usually store their food in corms. 

 In a corm the swollen stem contains food. The frameworks 

 of foliage leaves often remain attached from year to year, giving 

 a characteristic appearance to corms of diff"erent plants. These 

 are called tunics. A corm may be taken for a bulb until cut 

 across. New corms may arise as branches of old ones which 

 are active only one year or the corm may be perennial and give 

 rise each year to a new leafy shoot from the axil of an upper 

 leaf. In Testudinaria and Bowiea they become enormous. 



A potato is a tuber. It is the swollen end of an under- 

 . ground branch. That it is a stem may be seen by the " eyes " 

 which are buds, in the axils of reduced scale leaves. The 

 tubers become separated from the main plant and each bud 

 may produce a new plant vegetatively. A sweet potato gives 

 off" roots. The lower part is a tuberous root. The upper part 

 has more the habit of a stem, as new shoots for planting are 

 obtained from it. 



Stems, more or less swollen, which creep under ground or 

 are partly exposed, are called rhizomes. Plants with 

 rhizomes can spread without being much exposed to the sun. 



