Formed Constituents of Organisms 161 



possibly fungoid attack, but as they always yield sugar on 

 analysis they may further act as plant foods. 



Now, while, so far as at present known, each may be peculiar 

 to one or to a few related species of plant, it is often the case 

 that the same glucoside appears in genera or even families 

 with no special affinity. Thus, to cite only a few cases, liesper- 

 idin (C50H60O27), found in ripening fruits of the orange genus, 

 is also met with in the somewhat related genera Barosma, 

 Skimmiay and Toddalia. But it is also reported by Vogel 

 from Scrophidaria nodosa, a widely different type. Syringin 

 (C17H24O9 ) occurs not only in the related lilac and privet genera, 

 but also in the white locust (Robinia Pseudacacia). Coniferin 

 (C16H22O8) is not only largely typical of genera belonging to 

 the family Coniferae; it has been recognized in Asparagus, 

 in sugar beet, and in one of the Compositse. Quercitrin 

 (C36H38O20) as such, or as a nearly related substance, occurs 

 in genera of many families of dicotyledons. Are we then to 

 regard each case of occurrence of these as a long drawn heredi- 

 tary or as an acquired character .^^ 



Of the alkaloids, upwards of 200 have already been isolated 

 almost wholly from the higher flowering plants, but these 

 probably represent a smaller number than will in time be 

 recognized. They are all nitrogenous compounds, and a con- 

 tinuous serial relation can at times be traced between groups 

 of them, that indicate chemical substitution action. Thus 

 xanthin that occurs alike amongst plants and animals, me thy 1- 

 xanthin, caffein that is frequent amongst plants but is specially 

 rich in the coffee and cacao plants, also theobromine obtained 

 from the cacao plant, have an advancing formula-relation 

 thus: 



Xanthin C5H4N4O2 



Methylxanthin C6H6N4O2 



Theobrorain (dimethylxanthin) C7H8N4O2 



Caffein (trimethylxanthin) C8H10N4O2 



Similar but more complex relations can be traced in the 

 morphin-atropin series of vegetable poisons, as well as in others. 

 It will probably remain true that these compounds can cor- 

 rectly be called acquired characters for dicotyledonous plants, 

 since few have been observed in more primitive groups, and they 

 are also rare amongst animals. 



That these compounds have not suddenly and wholly devel- 

 oped however amongst dicotyledons is well brought out, if 

 one review the information given by Czapek (2Jf.: II, 259-316). 

 He there points out that a few occur amongst the fungi, wliich 

 seem frequently to show a higher and more intricate chemical 



G 



