Low. — On Haastia pulvinaris. . 157 



As has been before noted, the tip of each leaf is covered 

 with bag-hke projections of tissue ; these greatly increase the 

 assimilatory and respiratory surface without increasing the 

 size of the leaf. All the cells of the mesophyll contain 

 abundant chlorophyll, and both the upper and the under 

 surfaces of the tip are well calculated to perform the leaf- 

 functions, for stomata are very plentiful, and the cuticle is 

 extremely thin. The large air-space in the mesophyll of the 

 tip is also helpful in the aeration of the tissues. 



Thus Haastia is developed in two distinct ways — Firstly ,- 

 for protection against climatic rigours ; and, secondly, for the 

 performance of those vital functions that were threatened by 

 the first set of modifications. 



EXPLANATION OF PLATES XVII.-XIX. 



Plate XVII. 



A piece of Haastia pulvinaris, from above and from below. 



Plates XVIII. and XIX. 



Fig. I. A piece of Haastia pulvinaris ; natural size. 



a, stem stripped of leave.^. 

 Fig. II. Diagram showing branch system. 

 Pig. III. Gross-section of young stem, with leaf-base. 



c, epidermis ; c, cortex; r.^J., resin- passage. 

 Fig. IV. Section of year-old stem. 



j)hel., phellogen ; /., fissure in cork; scl., sclerenchyma : 

 s.t., sieve-tubes; c, cambium; v., wood-vessel; w.f., 

 fibre ; m.r., medullary ray ; s.v., spiral vessel. 

 Fig. IV. A, B, C, D, stages in formation of resin-passage. 

 Fig. V. Longitudinal section of year old stem. 



Fig. V. A, sclerenchyma found in phloem ; B, medullary ray, longi- 

 tudinally elongated, pitted; 0/, wood-fibre; tr., tra- 

 cheide ; p.v., pitted vessel ; s.v., spiral vessel. 

 Fig. VI. Transverse section of older stem. 

 Fig. VII. Transverse section of young root. 



a, piliferous layer; r.h., root-hair; pp., protophloem ; 

 2nd 'ph., secondary phloem; c, cambium; 2nd x., 

 secondary xylem ; 1st x., primary xylem ; x.v., vessel. 

 Fig. VIII. Longitudinal section of same. 

 Fig. IX. Transverse section of older root. 

 Fig. X. Longitudinal section of same. 

 Fig. XI. A, B, leaf ; natural size. 



A, upper surface ; B, lower surface ; C, A enlarged ; 



D, B enlarged ; E, C stripped of hairs ; F, D stripped 

 of hairs; 2J-> projections. 



Fig. XII. Section of base of leaf. 



V, upper surface ; d, lower surface ; p., phloem ; x., xylem ; 

 St., stoma ; c.l., chlorophyll layer ; b., base of hair. 



Fig. XIII. Longitudinal section of open leaf. 



a, terminal point ; h, young hair ; st., stoma ; a.c, air- 

 cavity ; r p., resin-passage of a bundle of network cut 

 transversely ; sp.v., spiral vessel, seen longitudinally. 



Fig. XIII. Ai, A.2, epidermis with stomata. 



B, hair ; b., small-celled base, with nucleus in each cell, n.. 



The other cells have pitted, pointed ends. 



