UNORGANIZED CELL-CONTENTS. 
23 
The following microchemical reagents are used in 
the study of the tannins and tannoids : Carbonates of 
the alkalies, chromic acid, cupric acetate, iron acetate, 
lime water, methylene blue, potassium bichromate, 
sodium wolframate, ammonium molybdate, bromine 
water. 
3. THE ALKALOIDS. 
The alkaloids probably arise in the protoplasm and 
later appear in the cell sap in combination with vari- 
ous plant acids, as malic, tannic and others, and may 
be precipitated by the so-called alkaloidal reagents. 
They occur in greatest amount in those cells which 
are in a potential, rather than an active condition, 
being associated with starch, fixed oils, aleurone grains, 
and other reserve products, in the roots, rhizomes and 
seeds. By reason of their existing in greatest amount 
when the food materials are also in greatest abun- 
dance, they are considered by some authors as a means 
of protecting the latter, in the plant, from the attacks 
of animals. They are found in fruits in greatest 
amount during the development of the seed, but after 
the maturing of the latter they slowly disappear, as in 
poppy and conium. The occurrence of alkaloids in 
the walls of the cells of certain plants, as in nux 
vomica, is no doubt due to their imbibition by the 
wall as a result of pathological changes in the cell. 
Many of the alkaloids which have been isolated by 
chemical means are in the nature of decomposition 
products of those already occurring in the plant, as 
certain of the alkaloids of tobacco, tea, coffee, cin- 
chona, opium, etc. The alkaloids are of more frequent 
occurrence in the dicotyledons than in the mono- 
cotyledons, and are rather characteristic for certain 
groups, as those of the genus Strychnos, Cinchona, 
Erythroxylon, Papaver, etc, 
