30 



PART I. MORPHOLOGY. 



12 



plane of insertion being usually transverse to the longitudinal 

 axis of the parent stem. 



The Hypopodium or Leaf-Base. The leaf-base commonly de- 

 velopes into a cushion of tissue, termed the pulvinus, which forms 

 the articulation by which the leaf is attached to the stem ; in the 

 Gooseberry the pulvinus developes into a spine. In many cases 

 the leaf-base is sheathing, and embraces a part or the whole of the 

 circumference of the node ; in the former case the leaf is said to 

 be semi-amplexicaul ; in the latter, amplexicaul (e.g. Grasses, 

 Onion, Fool's Parsley). 



The leaf-base sometimes produces a pair of opposite lateral 



Fto. 19. 4 Part of a sessile leaf of Grass (Poa trivialis) with the ligule t ; a the haulm ; 

 v the sheathing leaf-base ; I lamina of the leaf. B Leaf of a Willow (Soli* Caprea) ; a 

 stem ; 8 stipules ; p petiole ; / lamina ; fc axillary bud (nat. size). C Leaf of a Pea (Pisum 

 arvente) ; a stem ; 8 s stipules ; r mesopodium or petiole ; // leaflets ; rf r/ the upper leaflets 

 metamorphosed into tendrils ; r' end of the epipodium, likewise transformed into a 

 tendril. 



branches which are termed stipules ; when they are present the 

 leaf is said to be stipulate, and when they are absent, as is more 

 commonly the case, the leaf is said to be exstipulate. The stipules 

 are commonly winged appendages, similar in colour and texture to 

 the lamina, and they are then said to be leafy (Fig. 19 B, O), as in 

 the Willow, the Violet, and the Rubiacese where they are branched ; 

 and they are especially large in plants, like the Pea, where the 

 lamina is relatively small : in other plants, on the contrary, they 

 are small brownish scales, which fall off soon after the leaf is un- 



