252 Plant Physiology 



It has been noted that certain mineral constituents 

 migrate from old organs to the seed. In an analogous 

 manner organic products are accumulated. Storage may 

 also occur in bulbs, tubers, or aerial stems, roots, leaves, 

 and fruits. It is, of course, such natural storage organs 

 that have been seized upon particularly as food for man and 

 feeding stuffs for animals, and many of the plants possess- 

 ing these have been wonderfully improved through selec- 

 tion and breeding. 



A storage organ of available food-material has a phylo- 

 genetic reason for existence in the fact that it has to do 

 with subsequent growth and fruiting or with the propa- 

 gation of the species. Seeds, bulbs, tubers, and other such 

 structures are essentially propagative devices, and it is 

 not uncommon to find that they possess the capacity to 

 lie dormant for a period, or to withstand desiccation. 



141. Annuals, biennials, and perennials. - These 

 terms are used to imply one or more seasons of growth. 

 When an annual plant, like the oat, reaches maturity by 

 gradual, natural means, a very large part of the mobi- 

 lizable carbohydrate and protein material is deposited or 

 accumulated in the fruit or seed. The work of the plant 

 as a whole is done, and there is no great wastefulness of 

 readily used substance in the dead tissues. In the case 

 of a biennial plant, such as the sugar-beet, which has grown 

 for one season, the leaves have died, but the root has be- 

 come an organ for a great accumulation of sugar and other 

 food-materials. The next season by virtue of this stored 

 food the energies of the plant may be vigorously directed 

 toward the production and maturity of seed. 



The potato uses up during the early part of the season 



