MORPHOLOGY OF HIGHER PLANTS. 169 



disappear, as in poppy and conium. The occurrence of alkaloids 

 in the walls of the cells of certain plants, as in nux vomica, is 

 probably due to their imbibition by the wall as a result of patho- 

 logical changes in the cell (p. 437). 



Many of the alkaloids which have been isolated by chemical 

 means are in the nature of decomposition products of those nat- 

 urally occurring in the plant, as certain of the alkaloids of tobacco, 

 tea, coffee, cinchona, opium, etc. The alkaloids are of more fre- 

 quent occurrence in the dicotyledons than in the monocotyledons, 

 and are rather characteristic for certain groups, as those of the 

 genera Strychnos, Cinchona, Erythroxylon, Papaver, etc. 



While the microchemical study of the alkaloids requires 

 considerable technic, still, in certain drugs, their detection 

 is quite simple, as in nux vomica, strophanthus and hydrastis 

 (Fig. 292). 



The glucosides, like the alkaloids, are also probably formed 

 in the protoplasm. They are compounds of glucose and other 

 principles and may be classed as reserve products. In some 

 instances they readily separate out in the plant cell, as hesperidin ; 

 while others give characteristic color-reactions, as crocin, salicin 

 and coniferin, but in most instances they are with difficulty 

 detected by microchemical means. 



Gluco-alkaloids represent a class of compounds intermedi- 

 ate between the alkaloids and glucosides, possessing characteristics 

 of each. To this class belongs achilleine, found in various species 

 of Achillea, and also solanine, found in a number of species of 

 Solanum. (See pages 373-375-) 



Cell-sap Colors. — The majority of the other color-sub- 

 stances found in the higher plants besides the green and yellow 

 principles previously mentioned occur in solution in the cell-sap, 

 and may be in the nature of secondary substances derived from 

 the plastid pigments, or they may be produced directly by the 

 protoplasm. Upon making sections of the tissues containing cell- 

 sap color-substances, not infrequently strikingly contrasting col- 

 ors are observed in contiguous cells ; as in the petals of the poppy 

 and petals of certain lilies, where we find some cells of a deep 

 purple color, others of a deep red and still others of intermediate 

 shades. 



