











IN VEGETABLE BIOLOGY, 





505 



















assumed by the slime, as will be noticed on a reference to tig. 1 of 

 Plate XIY. There is one point in which this reaction is more 

 satisfactory than the others, inasmuch as it readily admits of the 

 preservation of the tissue treated by it ; the specimen shown 

 to-night has been mounted in glycerine for several months, and 

 its colours are still as brilliant as ever. 



Millon's reagent acts with Vegetable-Marrow callus as clearly 

 as does the just-mentioned test. To obtain it, however, care 

 must be taken to avoid over-boiling ; indeed, the best effect is 

 got at temperatures just below boiling ; but it boiling be con- 

 tinued even for a minute, the red colour is liable to disappear 

 (Plate XIV. fig. 2). 



But it is more difficult to prove that, in respect of the third 



■Marrow 



If 























previous observers have tried this reaction, their failure is scarcely 

 blameworthy on the score of remissness ; for who would dream of 

 upwards of an hour elapsing before the effect is brought about ? 

 And yet this is indeed sometimes the fact. Tou mount the 

 sections in copper sulphate, aud, after a little time, run in caustic 

 potash, but in almost all cases without any result for at least ten 

 minutes. Then perhaps a callous mass at the edge of the prepa- 

 ration will become very pale pink or bluish ; this will gradually 

 deepen into the colour of Plate XIV. fig. 3, or will become 

 lavender ; after a few minutes two or three more will follow suit, 

 until, finally, all are coloured. But it may happen that one hour, 

 °r sometimes even half as long again, must elapse before the 

 sl'ghtest change is caused in any of the callous masses. Wl 



] apse of time should 



occur is 



difficult to understand: possibly 

















■■ 



the method is at fault : and there may be some way of rapidly 

 getting the reaction; but if there is, it still remains to be 

 discovered. 



All the above-mentioned reactions were given in a very clear 

 manner by the slime of the sieve-tubes. The only difference 

 observed was that the respective colours were less pronounced, 

 'a consequence, apparently, of the less dense aggregation of the 

 s hme as compared with the callus. 

















I 







' 











"Wall oe the Sieve-tttbes 









(a) Proteid Reaction.— -Throughout the research this matter 

 was carefully attended to: the reason for this 



will 





TjIKN 





BOTANY, YOL. XXYII 



2N 







. 



■ 



■ 



4M 















r 









