26 MORPHOLOGY, OR COMPARATIVE ANATOMY. 



When a bulb flowers from its terminal bud in its first season of 

 growth, it is annual ; when it only strengthens itself by forming 

 scales in the first season, and flowers from the terminal bud in the 

 second, it is biennial ; when it flowers from an axillary bud, the 

 terminal bud may be developed in the same form indefinitely and 

 form a perennial bulb. 



The number of leaf-scales constituting the mass of a bulb varies much 

 in different plants : in Gayea and others there exists only one ; Allium 

 oleraceum has but two; the Garden Tulip and Crown Imperial have 

 comparatively few scales, while the Lilies and the Hyacinth (figs. 16 & 

 17) have numerous coats or scales. A little explanation is requisite as 

 to the terms annual &c. as applied to bulbs. We have an example of 

 what is called an annual bulb in the Garden Tulip. As planted in autumn, 

 it is a bud composed of four or five scales enveloping a central rudimen- 

 tary flowering stem which terminates the main axis. In the axil of the 

 outer scale there is an axillary bud. As the flowering stem is developed 

 the old bulb shrinks, while the axillary bud becomes more and more 

 perfect; so that, after the flowering season is over, it forms a new 

 bulb, to the side of which the withered remains of the old one are 

 attached. The terminal point of the new bud repeats the flowering, and 

 its outer scale (sometimes the next also) subtends an axillary bud destined 

 to become a new bulb in the next season. Such bulbs are sometimes 

 called pr adventitious , since the bulbous structure of any given axis is 

 formed before the true leaves and flower. The Crown Imperial (Fritilaria 

 imperialis) affords an example of a biennial bulb. Examined in the 

 autumn, it is found to consist of fleshy scales produced at the lower part 

 of the axis which has just flowered ; while a bud seated in the axil of the 

 innermost of these scales is already developed, and by the decay of the old 

 flowering stem has come to occupy the centre of the bulb. In the next 

 season this bud flowers : at first it is surrounded by the scales of its 

 parent axis ; but after the flowering is over, these very quickly shrivel up 

 and disappear, the axis which has j ust flowered giving origin at its base 

 to a number of scales replacing them ; and while the flowering stem 

 decays away down to these scales, a new axillary bud is developed in the 

 axil of its innermost or uppermost basal scale. Thus the bulb always 

 bears growths belonging to two seasons on the same axis : the nutrient 

 leaf-scales of each axis are developed upon it after it has flowered, and 

 serve for the support of the flower of the next axis. Such bulbs are 

 sometimes called postventitious, and may be termed definite to distinguish 

 them from the next kind. Perennial bulbs differ from the foregoing in 

 retaining the products of the condensed axes of several years in a healthy 

 vegetative condition. Thus, if we examine a bulb of the Garden Hyacinth 

 (fig. 17) when it is flowering by its terminal bud, we find the base of the 

 flowering axis surrounded by several leaves belonging to itself; the whole of 

 them stand in the axil of a scale belonging to the preceding year, which also 

 contains the short remnant of the flower-stalk of that year ; and to this 

 scale succeed several more, all belonging to that same axis ; these more- 

 over stand collectively in the axil of the innermost of a series of scales 

 belonging to the year before, remains of the flower-stalk of which are 



