250 



HUTCHINSON'S POPULAR BOTANY 



FIG. 306. ORIENTAI 



PLANE-TREE (Platanus 



orientMs.) 



A leaf-bud with its protecting 

 cap removed. 



' -" on the under surface at the points of contact, and 

 m from the upper surface new fronds arise (fig. 308). 

 /I It may be well to remark here that the plant 



^^. J9 known as the Butcher's Broom Helwingia (H. rusci- 

 d^ f mm flora), the flower-buds of which are seated on the 

 JWllr m[A foliage-leaf, is not to be classed with plants like 



/J^^ L Bryophyllum, and for this reason : the flower-buds of 



^y WtF Helwingia are not true epiphyllous buds. They do not 



j^J spring from the tissues of the leaves on which they 



are seated, but from the axes of the leaves, and with 

 these axes they are connected by strands, which are 

 simply disguised flower-stalks. In short, the buds 

 are not the result of protoplasmic activity in the 

 leaf-tissue, but spring from the rudimentary flower- 

 stalks, which differ from ordinary flower-stalks by being fused with the 

 midrib of the leaf. Another plant which somewhat resembles Helwingia 

 in this respect is Pfiyllonoma ruscifolium, a Mexican shrub ; but the leaf 

 in this case is surmounted by a long acumen below the base of which the 

 flowers appear. 



The manner in which the young rudimentary 

 leaves are arranged in the leaf-buds in scientific 

 parlance, their vernation or prefoliation forms an 

 interesting study. Each species of plant has its 

 own particular method of folding its unexpanded 

 leaves, and a definitive term is applied to each. 

 In the Ferns (Filices) the fronds are coiled from 

 tip to base (drcinate) ; in the Grasses (Graminece) 

 from one side to the other (convolute) ; in the 

 Violet ( Viola) the lateral margins are simultaneously 

 rolled inwards towards the midrib (involute) ; in the 

 Cowslip (Primula) and Dock (Rumex) a similar roll- 

 ing is seen, but outwards (revolute) : in the Currant 

 (Ribes) and Beech (Fagus) the leaf is plaited with 

 several folds lengthwise (plicate) ; and in the Cherry 

 and Plum (Prunus) it is folded flat from the midrib 

 with the edges in contact (conduplicate). These 

 distinguishing names being descriptive are easily 

 acquired ; but we do not lay stress upon them just 

 now. The fact that we would emphasize (and it is 

 very remarkable) is this that the tissues forming 

 the leaves are manufactured folded up I We can 

 understand a loom weaving a material, and then 

 folding it ; but here is the material folded up, and 

 unfolding only when it is all woven ! 



FIG. 307. TULIP-TREE 

 (Liriodendron tulipifera). 

 Young leaf lying be 

 stipules, on 



if which 

 removed . 



bee 



