STRUCTURE OF PLANTS. 53 



of this green colouring matter, which is produced, in especial 

 abundance, in the various kinds of indigo (Indigofera 

 tinctoria and anil,} in woad, (Isatis tinctoriaj and the 

 dyer's knot-grass (Polygonum tinctorium). 



In some cells we find exceedingly elegant crystalline 

 formations, consisting either of single crystals or bundles 

 of needle-shaped ones, or of a number of them collected 

 into a little crystalline nucleus (PI. n, Fig. 1.) 



The contents of the vegetable cells, however, which are 

 most interesting to mankind, are those which furnish 

 him with necessary food, agreeable refreshment or stimu- 

 lating spices, and not less important are those substances 

 which, administered to the diseased organism, bring back 

 the uninjured capability of enjoying anew the rich gifts 

 of creative Nature. This field of observation is one of 

 extraordinary extent, and not yet nearly sufficiently 

 explored ; nevertheless, the researches which have already 

 been followed out, have led to an interesting law, namely, 

 that those plants which are nearly allied in their external 

 form, also contain similar or closely connected substances 

 in their corresponding organs. Thus there are whole 

 families in which all the plants are more or less poisonous, 

 as the Nightshade plants, the allies of our potato and 

 tobacco ; while others are insipid, and tasteless, and 

 therefore devoid of any peculiar substance, such as the 

 allies of our garden pink. It would lead us too far, to 

 attempt to enumerate here all the different matters, and 

 where they occur in the vegetable world ; we must content 

 ourselves, therefore, with a few general observations, and 

 a more minute examination of some of the most interesting 

 substances. 



The substances which we find in the cells of plants, 

 may be divided into those soluble in water and the 



