i893. PLANT NUTRITION. 23 



Two different batches of Tropaeolum leaves picked after the same 

 amount of isolation were found to contain 6*408 and 6-545 per cent, 

 of starch respectively, results which are representative of the accuracy 

 which can be attained by their method. 



Estimation of the starch in the leaves of sunflower while 

 attached to the stem, at five a.m. and again at five p.m. on a fairly 

 bright day, showed an increase of i"4 grams of starch per square 

 metre during this period, while the total assimilation-products 

 actually formed during this time, estimated from the dry weight of 

 similar leaves separated from the stem and their petioles immersed 

 in water, was over twelve grams per square metre. It is here seen 

 that if Sachs' view is correct — that all the assimilated materials pass 

 through the form of starch — the formation of the latter substance and 

 its dissolution must be carried on at an exceedingly quick rate. It is, 

 however, far more probable that much of the assimilated material 

 passes out of the leaf into the stem of the plant without ever being 

 organised into starch by the chloroplasts. 



Messrs. Brown and Morris go on to discuss the occurrence and 

 periodic variation in the amount of diastase present in leaves, and in 

 this direction they have achieved much success. Incidentally, it may 

 be observed that the whole of their work arose out of the discovery of 

 diastase in dry hops when they were prosecuting an enquiry into the 

 cause of secondary or " cask fermentation " in beer. 



The function of the ferment diastase in the breaking down of 

 starch into the soluble substances sugar and dextrin when seeds are 

 allowed to germinate, has been recognised almost from the time of its 

 discovery and isolation by Kirchoff, Payen and Persoz, and 

 Dubrunfaut at the beginning cf this century, and a study of this 

 dissolution of starch led to the generally expressed belief that the 

 same or a similar ferment is concerned with the disappearance of 

 starch from the leaf chloroplasts. 



Attempts, however, to isolate diastase from green leaves were not 

 made until about 1877, when Kosmann and Baranetzky took up the 

 work. Small traces were found in the leaves of various species of 

 plants by both observers, and Baranetzky expressed the opinion that 

 the smallness of the amount present at any one time was to be 

 attributed to its being used up as fast as it is produced. 



Brasse, in 1884, also conclusively proved its presence in leaves, 

 though Sachs in the same year, in his paper on assimilation, was unable 

 to decide whether the dissolution of starch in the leaf is due to some 

 special power of the chloroplast, or to soluble ferments. 



Wortmann, in 1880, from experiments of the most questionable 

 character, concluded that diastase is missing from practically all 

 leaves, and even when present plays no part in starch dissolution, the 

 process being attributed by him to the action of the living contents 

 of the cell. 



Messrs. I5rown and Morris find, however, that, instead of leaves 



