STRUCTURE OF MODIFIED SHOOTS 137 



leaves and a flowering shoot, and the bases of the leaves 

 thicken and store food, after which the green portions die 

 away. 



When digging up Tulip bulbs look out for curious forms 

 like the one shown in Fig. 85, 3. In this case an axillary 

 bud has pushed its way through the old outer scale and 

 grown downwards in the form of a long, tubular, stalk-like 

 bulb. A section through this shows a small bud at the 

 lower end (dr.b). If such a bulb is carefully potted and 

 its behaviour studied, you will find that adventitious roots 

 are given off from the small bulb, foliage-leaves grow out 

 into the air, and the tubular attachment to the parent bulb 

 dies, leaving a young bulb at a lower level in the soil than 

 the parent. 



Why should some buds remain short and grow alongside 

 the parent bulb while others elongate and push their way 

 deeper into the soil ? Seeing that the buds are axillary, 

 and therefore produced successively at higher nodes, what 

 would be the position of the young bulbs in the soil after 

 several seasons' growth ? 



In consequence of this tendency to ascend in the soil, 

 bulbs would eventually come too near the surface for 

 successful development. We have seen various devices by 

 means of which plants maintain a suitable depth in the 

 soil, and the method adopted by the Tulip is to produce 

 down-growing buds called ' droppers ', some of which, 

 especially in seedling plants, may be from three to nine 

 inches long. 



The means by which seedlings of bulbous plants descend 

 in the soil and eventually reach the depth requisite for 

 successful growth may be well studied in the Bluebell or 

 Wild Hyacinth. In winter and in early spring many 

 stages in the process can be found among the humus of the 

 woods, and a number are shown in Fig. 87. You will find 

 that the blue-black seeds germinate freely among the dead 



