viii CONTENTS 



CHAPTER PAGE 



(II) 8. Secretion and excretion 620 



Water exudation 620 



Secretion of oils, resins, and mucilage 622 



Crystals and cystoliths 625 



9. Accumulation of water and food 627 



IO. Miscellaneous structures and relations 636 



Run-off . 636 



Reproduction 636 



Conductive tissues 638 



Mechanical tissues 639 



Leaf tendrils .......... 640 



Petioles 640 



Stipules 641 



Scale leaves . 642 



III. Stems . 645 



1. Stems as organs of display 645 



Display of foliage leaves . 646""** 



Lianas 651 



Epiphytes 657' 



Synthesis and aeration in stems 660 



Display of reproductive organs ....... 667 



2. Stems as reproductive organs , 667 



Rhizomes 667 



Runners ........... 672 



Tubers, corms, and bulbs 674 



Water plants . . 676 



3. Conductive tissues 678 



4. Mechanical tissues ......... 696 



5. Protective relations of stems 704 



Bark ............ 704 



Cork -70S 



Stem habits 709 



Duration ........... 717 - 



6. Accumulation of water, food, and waste products . . . .718* 



Air and water 718 



Foods 719 



Latex 720 



Mucilage, oils, resins, crystals, tannin, and dyes . . . 723 



7. Variation in form . . . 725 



Elongation in aerial stems - . . 725 



Elongation in aquatic stems ....... 728 



Elongation in stems submerged by sand 729 



Dwarfing 730 



Asymmetric stems . . - . . . . . . . 734 



Periodicity in development 735 



Origin of trees . . . . . . . . . . 737 



Spinescence 741 



Tuberization . . . . . . . . . . 744 



Correlation ; regeneration ; polarity 747 



JV. Saprophytism and symbiosis . . . f , f . . . 752 



