20 



STRUCTURAL AND PHYSIOLOGICAL BOTANY. 



Terete 74 ; half-terete 75 ; compressed 76 ; piano-compressed 76 ; two-edged 77 ; acute- 

 angled 78 ; obtuse-angled 81 ; triangular 83 ; quadrangular 81 ; quinquangular 82 ; 

 octangular "> ; multangular 80 ; triquetrous 78 ; quadriquetrous 79 ; obscurely 

 triquetrous 85 ; trilateral 86 ; quadrilateral 87 ; quinquelateral 88 . 



V. LEAF-BUDS. 



163. Buds are of two kinds, Leaf-buds and Flower-buds. 



164. LEAF-BUDS (Bourgeon, Fr.) consist of rudimentary 

 leaves surrounding a growing vital point, the tissue of which 

 is capable of elongation, upwards in the form of stem, and 

 downwards in the form of root. 



165. FLOWER-BUDS (Bouton, Fr.) consist of rudi- 

 mentary leaves surrounding a fixed vital point, and 

 assuming, when fully developed, the form of floral 

 envelopes or sexual apparatus. 



166. Notwithstanding this difference, a leaf-bud 

 sometimes indicates a tendency to become a flower- 

 bud ; and flower-buds frequently assume the cha- 

 racters of leaf-buds ; Ex. Monstrous Pears. 



167. In appearance a leaf-bud seems 89 to be a 

 collection of scales arranged symmetrically one 

 above the other. These scales are the rudiment- 

 ary leaves. The centre upon which they are placed 

 is cellular substance coated with a thin stratum 

 of spiral vessels, and these two parts answer to 

 the pith (98) and the medullary sheath (104) in 

 Exogens. 



168. By the growth of a leaf-bud a branch is formed ; and 

 the scales gradually change into true leaves as vegetation ad- 

 vances 92 . 



169. Sometimes they separate spontaneously from the stem 



