ANALOGY OF PLANT OKGANS. 53 



leaf or else are stipules. The former are by far the most numerous ; 

 such as bulb-scales, shcathinpj scales of creeping grass-stems, 

 and the nulinieutary scales of the "eyes" of potatoes. Eut the 

 violet and strawberry furnish illustrations of stipules forming scales 

 on rliizomes. 



AVith reference to their functions, they may be (1) rudimentary 

 and presumably useless as on potatoes ; (2) protecting the bud 

 included within them ; and (3) reservoirs of nutriment as on bulbs. 



Bud-scales are homologous with several structures ; they may 

 be:— 



1. Stipular, as in the lime, elm, oak, and beech. 



2. Laminar, as in the lilac and willow. 



3. Ft'do/ar, as in the horse-chestnut and cuiTant. 



4. Petiolar and stipular, by cohesion, as in the plum. 



5. Laminar and stipular, but free, as in the hawthorn. 



The functions of bud-scales are mostly the same, whatever be 

 their origin ; namely to protect the delicate parts within. To 

 enhance this function they are often provided with hair, either silky, 

 as in the beech and willow, or looolhj, as in the apple. The hair may 

 either densely clothe the leaf, as in the apple, or else the stipules 

 may be hairy as in the willow. The hair acting as a non-conductor 

 enables the heat due to respiration to be retained. Externally they 

 may be resinous, as in the horse-chestnut. 



The only additional function they may assume is that of storing 

 up nourishment for the bud, when it can become detached and 

 maintain an independent existence, as in Lilium bulbiferuin, Dentaria 

 hulhifera, etc. 



2. The true Leaf Region. Stipules. — The true origin of stipules 

 has not yet been satisfactorily or definitely determined in every case. 

 That they are foliar or phyllomes is generally admitted, but 

 "whether they are in all cases organicalli/ one with the leaf, or 

 totally independent of it, in many cases is not yet decided."^ 



With reference to the duration of stijmles, they are persistent or 

 deciduous ; and with regard to their character, they may be (when 

 persistent) as follows: — 



1. Foliaceous and lateral in position, e.g. Pisitm. 



,, axillary ,, ,, Melianthus. 



,, interpetiolar ,, ,, Galium. 



2. Membranous . . . • >> Pelargonium. 



3. Scarious ....,, Illecebracim. 



4. Spinescent . . . • >> Acana (species). 



5. Cirrhose . . . • ,, iSmilax. 



6. Bracteiform . . . . ,, Viola, Fragraria. 



* According to Griffith ('Notulnc') stipules are (1) petiolar or "extensions of 

 the petiole," as in Xandina domestica (Part I, p. 226) and in the Ochrea of Poly- 

 gonacem, such being, according to him, "a mere dilatation of the petiole, the 

 margins of the dilated part cohering and forming a sheath ; " but it is otherwise 

 regarded as axillary by cohesion of two stipules between the leaf and the stem, 

 and cohering on the further side of the stem as well, so forming a tubular 

 sheath. Again, stipules may be (2) ' ' considered as the lowermost pair of pin - 

 nules," as in Bauhinia and other leguminous plants (p. 228). Lastly, they may 

 be (3) "nothing but the lowermost lobes of the leaves," as in Passijlora (p. 229) 



