150 THE BOOK OF NATURE STUDY 



When the bulb of a plant from which the shoot has grown 

 up is compared with the bulb at the time of planting, great 

 changes are apparent. It is rooted in the soil and partly by the 

 escape of the roots, partly by the increase in size of the enclosed 

 parts, the brown protective scale is more or less ruptured. The 

 storage scales within, which were plump and white, are now 

 shrivelled and drying up. The food material stored in them 

 has been removed and utilised in the growth of the shoot and 

 flower. The use of these storage scales is over, and they will 

 now gradually decay. 



The development of the bulb or bulbs, which will remain in 

 the ground after the rest of the plant has decayed, is already 

 far advanced. These new bulbs arise from buds situated in the 

 axils of the inner storage scales of the parent bulb. The bud 

 enlarges and develops into a bulb like that with which we started. 

 As the new bulbs grow they force apart and rupture the withered 

 scales of the old bulb. On dissecting one of the developing bulbs 

 the protective outer scale, which is still soft, and the series of 

 storage scales can be distinguished. In some cases the protective 

 scale will be found to bear a small green leaf-blade, and this shows 

 that the overlapping bulb-scales correspond to the transformed 

 bases of leaves which completely surround the stem. The food 

 material, which is being stored in the growing bulb or bulbs, is 

 formed by the activity of the green foliage-leaves exposed to the 

 light, and is conveyed downwards through the stem into the 

 bulb-scales, where it accumulates as starch. Since the growth of 

 the shoot took place at the expense of the material stored in the 

 old bulb, practically the whole of the substance manufactured 

 by the foliage can be saved and stored up in new bulbs. The 

 Tulip, like many plants which flower early in the season, depends 

 for its growth on material manufactured in the preceding season. 



In some cases only a single new bulb is formed, but usually, 

 under favourable conditions of nourishment, two or three bulbs 

 of considerable size develop, and sometimes other smaller ones. 

 When the old bulb decays these become isolated from one another 

 in the soil, and so form independent plants in the next season. 

 The formation of the new bulbs thus serves to increase the number 

 of individuals, and is a most efficient means of vegetative repro- 



