160 A TEXT-BOOK OF BOTANY. 



seeds, or leaves. Furthermore, the amount is greatest at certain 

 stages of development, as in the fully ripe seeds, more or less 

 immature fruits, during the resting periods of roots and rhizomes, 

 and in leaves when photosynthetic processes are most active. 

 They occur in greatest amount in those cells which are in a poten- 

 tial rather than an active condition, being associated with starch, 

 fixed oils, aleurone grains, and other reserve products in the 

 roots, rhizomes, and seeds. 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 the opium poppy and 

 conium. 



The alkaloids probably arise in the protoplasm, although they 

 may also be formed from the decomposition of protein substances. 

 The fact that asparagine, a weak base, is usually present when 

 the proteins are being formed from the protoplasmic substances 

 and is also present when the proteins are being used in the growth 

 of the plant, as during the germination of seed, would seem to 

 indicate that both views are more or less tenable. The studies 

 of Lotsy on Cinchona showed that alkaloids are formed in con- 

 nection with photosynthetic processes and that they are subse- 

 quently stored for the use of the plant. On the other hand, 

 it is rather interesting to note that when cinchona trees are 

 grown in the hot-house they do not produce any quinine, and, 

 again, it is said that the conium growing in Scotland does not 

 contain any coniine. From these observations we must conclude 

 that alkaloids are produced only under certain conditions, and 

 that they are not essential metabolic substances. The fact that the 

 presence of alkaloids may be demonstrated in the thick- walled 

 cells of the endosperm in ilux vomica has led some investigators 

 to conclude that they may arise in the cell-wall. The occurrence 

 of alkaloids at this point is due to their imbibition by the wall, 

 just as other soluble cell contents are absorbed, especially upon the 

 death of the cell. 



MICROCHEMISTRY OF AL K Ai.oiDS.- -The alkaloids occur in 

 rather large quantities in a number of plants. Seldom do we 

 find them in the form of crystals in the plant cell. Crystals of the 

 alkaloid Piperine are not infrequently observed in the oil secre- 

 tion cells of the endosperm of Piper niyrum (Fig. 94, A}. The 



