IN THE MOTOR ORGANS OF LEAVES. 



25 



appear to be the same, the tint being determined by the relative acidity or alkalinity 

 of the medium. Hence blue flowers usually pretent a more or less purplish or reddish 

 tinge in natural fading and when under the influence of chloroform; whilst red ones, 

 on the contrary, loso their brilliancy and may even become almost colourless (like those 



of Erythrma stricta) und 

 related to intense 



The colour in Erythrina stricta is evidently 



to intense acidity of the medium; for even perfectly neutral media reduce it very 



much, just as strong alkalis act on other red tissues; while the alcoholic extract dem a nd s 

 an excessive addition of acid ere it reacquires a scarlet tint. Some blue flowers, such as 

 those of the blue variety of CUtoria Ternatea, present an exception to the rule enunciated 

 above, as they retain an intense blue colour during normal fading and exposure to 

 chloroform, and they yield brilliant pure blue infusions and extract* on boiling and 

 immersion in alcohol. This is not dependent on any peculiarity in the essential < onsti- 

 tuents of the colour, for the addition of acids to the blue extracts or infusions at onoe 

 causes them to assume a beautiful red colour; but must apparently bo due to the cell-sap 

 normally containing a relative excess of fixed alkaline constituents— an assumption 

 which is favoured by the very feeble acidity which the freshly expressed sap presents. 

 The extremely fugitive nature of the alkaline constituents in some other casts is most 

 strikingly exemplified in cases where flowers of Ipomoca kkkracea are killed by means of 

 exposure to low temperatures, as the following experiment shows 



Experiment XIII.—A fully expanded and normally coloured flower wai 



ed 



m a 



metal box, and the latter was then buried in a mixture of pounded ice and 



where it remained for an hour and a half. At the close of this period the flower 

 remained fully expanded and retained its original colouring, but was frozen and rigid. 

 On removal from the box immediate collapse occurred, and the colours of the normally 

 blue and red areas at once changed, the former becoming violet and the latter 

 ochreous. The white coloured portion at the base of the tube retained its colour 

 somewhat longer, and then, like the red ones, became ochreous, the blue portions having 

 meantime passed on from purple to dull red. 



Immersion of flowers of the same species in boiling water is followed immediately 

 by total collapse and similar changes in colour, but the results in this case are not so 

 striking, as they are not so conclusively ascribable to mere ce nation of protoplasmic 

 activity' as where they follow exposure to cold. The absence of collapse and the reten- 

 tion of the normal colour in the latter case, so long as the tissues remain frozen, must 

 apparently be due to the cell-sap being congealed so rapidly that no appreciable escape 

 of liquid or discharge or decomposition of the fugitivo alkaline or acid constituents 

 present in it have time to occur. The process of rapid congelation not only arrests the 



ire of the products of protoplasmic activity on which the turgescence and 

 colour of the tissues depend, but it for the time being retains those which are present 

 in the sap at the moment at which congelation occurs. ^ On the tissue thawing, an 



- loss of turgescence occurs, and this is accompanied by the escape or decom- 



manufact 



med 



position of the products of certain constituents of the cell-sap to which its normal 

 lour is due. It would be hard to find a more striking instance of the coincidence of 



loss of turgescence with alterations in the chemical constitution of cell-sap. 



It is only where the colours of the tissues depend on the presence of dissolved 

 i nts tbe tmts of which are determined by the presence of fugitive acid or alkaline 



substance's that they serve as satisfactory indices to the occurrence of chemical changes 



Ann. Koy. Bot. Gard. Calcutta Vol. VI 







