CHAPTEE IX. 



OPEN COLLATERAL VASCULAR BUNDLES LATEX BICOL- 

 LATERAL BUNDLES STRUCTURE OF SIEVE-TUBES THE 

 THICKENING OF DICOTYLEDONOUS STEMS. 



PRINCIPAL MATERIALS USED. 



Runners of Ranunculus repens ; fresh, or in alcohol. 



Stems of Clielidonium majus ; in alcohol. 



Roots of Scorzonera; fresh, or in alcohol. Or, Dandelion. 



Stems of Euplwrbia splendens, or E. jacqiiince flora ; in alcohol. ' 



Stems (not young) of Bryonia dioica, or other Cucurbit ; in alcohol. Also 



fresh. 



The same fixed with boiling water and preserved in alcohol. 

 Twigs of Aristotochia Sipho, i to ^ thick ; also thicker twigs ; preferably in 



alcohol. Or, young plants of Ricinus communis, Helianthus annuus, or 



H. tuber osus. 



PRINCIPAL BE AGENTS USED. 



Chlorzinc iodine Potash Aniline blue Soda corallin Sulphuric acid 

 Phloroglucin and hydrochloric acid. 



Stem of Ranunculus repens. As a first example for the study 

 of the open collateral vascular bundles, which are peculiar 

 to Dicotyledons, \ve select the creeping stems (runners) of 

 Ranunculus repens, the creeping Buttercup. The cross-section 

 shows that the vascular bundles are separate from one another, 

 but arranged in a simple circle, so that the ground-tissue, as a 

 whole, shows a central portion, or pith, an external portion, or 

 cortex, while between the bundles are broad strips of ground- 

 tissue which we may call the medullary rays, This distinction 

 we will discuss in greater detail hereafter. The ground-tissue, 

 generally, consists of rounded cells, which become smaller towards 

 the periphery of the stem, contain chlorophyll grains, and have 

 between them large intercellular spaces. The epidermis forms 



(121) 



