6o 



THE VEGETATIVE SHOOT 



not needed for the plant's immediate requirements is trans- 

 ferred to lateral axillary buds below ground, and is there stored. 

 These buds consequently grow rapidly and become young 



daughter bulbs; one of them is 

 shown at n in course of development. 

 Bulbs like the onion, tulip, and 

 hyacinth, which have broad, concave 

 scales arranged in such a manner 

 that the outer ones completely en- 

 close those within, are known as 

 tunicated bulbs. In lilies the bulb 

 scales are not so broad, and are 

 arranged to overlap each other like 

 the tiles on a roof : such bulbs are 

 said to be imbricated. 



Ex. 32. — Cut a longitudinal section 

 through a young onion plant when the 

 bulb is well formed. Watch the develop- 

 ment of a young plant into an old bulb. 

 Cut sections of k mature onion bulb and 

 compare its internal structure with that of 

 a Brussels sprout. 



Ex. 33. — Examine old onion bulbs which 

 have been kept all winter and allowed to 

 sprout. Note the number of separate sets 

 of green leaves produced by it. Cut it 

 open and examine the origin of the latter. 



Ex. 34. — Cut longitudinal sections of 

 tulip, hyacinth, snowdrop, and narcissus 

 bulbs. Note the stem, the number of 

 scales, and their relative thickness in each ; 

 also the presence or absence of rudimentary 

 flowers and axillary buds. 



Ex. 35. — (i) Examine the structure of 

 a crocus corm in autumn. Pull off the outer 

 scaly leaves and observe the position and number of the buds on the thickened 

 stem. (2) Cut longitudinal sections of a corm. (3) Examine a corm in 

 bloom, and observe the roots, remains of old conns, foliage and membranous 

 scale-leaves, and number and position of the flowers. Compare with Fig. 23. 



Fig. 25. — Section of a tulip 

 flower, t Stem on which are fleshy 

 bulb scales, ; p flowering stem 

 bearing green leaves, e ; a ovary ; b 

 stamens ; c perianth of the flower ; 

 n bud developing into a new bulb ; 

 s small dormant buds. 



