76 
ORGANOGRAPHY. 
BOOK I. 
grow freely, and after a time will emit small roots from just 
above its union with the stock ; at the time when these little 
roots are formed, let the shoot be cut back to within a short 
distance of the stock, and the little roots will then, in conse- 
quence of the great impulsion of sap into them, become 
branches emitting leaves. 
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 Willoios 
they are covered with a thick down ; in Popidus 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 imperfectly 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 such plants as Viburnum prunifolium. 
Magnolia acuminata, Liriodendron Tulipifera, and jTIscuIus 
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 
membranous 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 bulb ; 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 
