THE ORGANIZATION OF THE PLANT 



87 



of four-o'clock 

 cot, cotyledon ; 

 caw, caulicle ; 

 end, endosperm 



Life cycle of plants. The life cycle of some plants is com- 

 pleted in a single season. They spring up, flower, produce 

 v-- -can their seeds, and disappear within the interval 

 \-plu of a few weeks or months. On the other 

 \-cot l iail cl, some of the lofty trees that still inhabit 

 ^ the earth have been growing for many hun- 



FIG. 79. Seed dreds or even thousands of years. As regards 

 of honey locust their length of life, however, plants may be 

 cau.caolicle ; phi, t |j v ided into three groups annuals, biennials, 



plumule ;co,coty- 



ledon ; end, endo- and perennials. An annual is a plant that 



sperm; tes, testa completeg itg life cycle within 



a year. This may occur during a single grow- 

 ing season, as in the radish, when it is called 

 a summer annual ; or the plant may spring up 

 in autumn, live through the winter, and fruit 

 in the spring, as in some varieties of wheat, 

 thus becoming a winter annual. Several of 

 the common summer annuals of our gardens may be treated as 

 winter annuals. Lettuce and spinach are sometimes grown in 

 this way. It is clear from the behavior of these plants that they 

 do not die from the cold but are killed by fruiting. Biennials 



differ from annuals in 

 -- end -& 



that they require two 

 growing seasons to 

 complete the round of 

 their existence. The 

 first year they store up 

 much food, which they 

 use the second year in 

 pioducing seeds. Car- 

 rots, salsify, and beets 

 are biennials. In re- 

 gions with a long growing season the line dividing an- 

 nuals from biennials breaks down more or less completely. 



.cot. 



I .plu 



FIG. 81. Grain of corn 



The fruit and seed of a monocotyledon, end, endo- 

 sperm ; cot, cotyledon ; pin, plumule ; cau, caulicle 



