458 CVAXOliKXES*l.s IX I'LAXTS, 



Alocasia, the aetiuu is ueitlior regular uor abuiKlaut,. ^vliile in numerous others the 

 enuilsiu acts rajiiclly aud freely, llctfrudetidruii belongs to the latter group. 



T.vui.K D. — When amygdalin is boiled with dilute mineral acids such as 

 hydrochloric or sulphuric, it is hydrol\sed. When the latter are replaced by 

 organic acids sucli as tartaric, no deeompositiou of the glucoside takes place. 

 Tartaric acid, like the mineral acids, has been shown to prevent the action of 

 enzymes entirely. For these reasons it is used to detect the presence of any 

 hydrocyanic acid which may exist in the uncond)ined state, that is, not in a gluco- 

 side. Various workers have recorded the presence of noa-glucosidal hydrocyanic 

 acid in plants, but the writer has not yet detected it in a single instance. 



Gexeral. — (a). There are some plants in which the cyanogenetic glucoside 

 increases to a maximum amount during the earlier and vigorous period of their 

 metabolism. It then gradually becomes less till towards the end of the season it 

 has dwindled to a relatively snuill amount and sometimes has disappeared entirely. 

 In such plants the glucoside is stored only temporarily, it is used up during the 

 acti\e vegetatixe periods, and there is none found in the ripe seeds. 



Examples of these jilants are the Sorghum, which in the ripe stage is left 

 with an amount of dhurrin ef|uivalent to about 14 mgs. % of hydrocyanic acid 

 (Brunuich), and sometimes with none (Treub) ; aud the Lotus of Egypt, which 

 >ields 345 mgs. ^o of hydrocyanic acid during the height of its vigorous growth, 

 but when its seeds are ri}ie it yields no hydrocyanic acid. Agaiu. I\il)es (cur- 

 rants) and others gi-adually lose their hydrocyanic acid compounds. 



{})). There is another group of cyanogenetic plants in which the hydrocyanic 

 acid remains almost constant throughout the whole .period of growth. This in- 

 cludes I'ussifJora sp)>., Samhucus nigra, Phuseolus lunatns and Imligofera yale- 

 r/oirle.i. Although it is diflicult to compare these plants with the e\ergreen tree 

 Ileterodendron, it may be noted from Table B that the latter plant contains ])rac- 

 tically the same amoimt of glucoside in winter as in summer. 



(c) When cyanogenetic plants are collected and spread out to dry. two 

 courses are followed: one in which the glucoside gradually disappears, the other 

 in which it remains unchanged for very long periods. 



As examples of the first course may be mentioned t'ljiiodon iiicompletiis (blue 

 couch gi-a.ss), which shows during four weeks' drying in the open air, a gradual dim- 

 inution to zero; -Aloeasia macrorrhiza, fium which no hydrocyanic can be obtained 

 after a few weeks ; .nnd Sorghum, which loses about three-quarters of its glucoside 

 under these conditions. As an example of the second course we note from Table 

 B that samiile ii. during four months remained almost constant, and sample iii., 

 lying openly for twelve months also remained about the same. It may be stated 

 then that though jilants like Sorghum may be rendered much less deleterious by 

 air-drying or curing, the foliage of Ileterodetidroti cannot be treated in this way 

 with any a<lvautage. 



The enz_\inc in the dried leaves of Heterodendron is apparently i|uite inactive 

 at the ordinary temperature, hence the constancy of the yield of hydrocyanic acid 

 during long jicriods (d' drying. In this respect it differs from the enzymes of 

 most other plants— for instance. Brill found that his samples of Pomjium edule. 

 owing to the action of a very active enzyme, continued to lose hydrocyanic aci I 

 from the time they were cut. 



The quantity of hydrocyanic acid evolved from Heterodendroii is relatively 

 very large. It nmv be conipareil with thai Ironi some of the richest cyanogcne- 



