CHAP. II. STEM. 59 



The leaf-buds of the deciduous trees of cold climates are 

 covered by scales, which are also called tegmenta ; these afford 

 protection against cold and external accidents, and vary much 

 in texture, thickness, and other characters. Thus, in the 

 Beech, the scales are thin, smooth, and dry ; in many Willows 

 they are covered with a tliick down ; in Populus halsamifera 

 they exude a tenacious viscid juice. In herbaceous plants 

 and trees of climates in which vegetation is not exposed to 

 severe cold, the leaf-buds have no scales ; which is also, but 

 very rarely, the case in some northern shrubs, as Rhamnus 

 Frangula. 



The scales of the bud, however dissimilar they may be to 

 leaves in their ordinary appearance, are nevertheless, in 

 reality, leaves in an miperfectly formed state. . They are the 

 last leaves of the season, developed at a period when the cur- 

 rent of vegetation is stopping, and when the vital powers have 

 become almost torpid. That such is really their nature is 

 apparent from the gradual transition from scales to perfect 

 leaves that occurs in sucli plants as Viburnum prunifolium, 

 Magnolia acuminata, Liriodendron tulipifera, and ^JEsculus 

 Pavia ; in the latter the transition is, perhaps, most satisfac- 

 torily manifested. In this plant the scales on the outside are 

 short, hard, dry, and brown ; those next them are longer, 

 greenish, and delicate ; within these they become dilated, are 

 slightly coloured pink, and occasionally bear a few imperfect 

 leaflets at their apex ; next to them are developed leaves of 

 the ordinary character, except that their petiole is dilated and 

 membi'anous like the inner scales of the bud; and, finally, 

 perfectly formed leaves complete the series of transitions. 



Among the varieties of root is sometimes classed what 

 botanists call a hulh ; a scaly body, formed at or beneath the 

 surface of the ground, emitting roots from its base, and pro- 

 ducing a stem from its centre. Linnaeus considered it the 

 leaf-bud of a root ; but in this he was partly mistaken, roots 

 being essentially characterised by the absence of buds. He 

 was, however, perfectly correct in identifying it with a leaf- 

 bud. A bulb has the power of propagating itself by deve- 

 loping in the axils of its scales new bulbs, or what gardeners 

 call cloves, {Cmjeu, French; Nucleus and Adnascens of the 



