26 Scientific Proceedings, Royal Dublin Society. 



Stahch. 



Marchal (6) has shown that P. juniperum, arid, in fact, all the starch- 

 building mosses examined, can build up. starch, wh.en artificially fed with 

 solutions of varying concentration of sucrose, glucose, maltose, and lactose; 

 but from the experiments it is impossible to come to any conclusion as to 

 their relative efficiency. In his work he used percentages by weight, but it 

 seems doubtful whether this does not put sucrose at a disadvantage in 

 comparison with the hexoses. In discussing the starch of P. commune, the 

 starch in the lamellae of the leaf and the starch in the stem must be 

 distinguished. The question that naturally presents itself is whether the 

 same sugar is concerned in the formation of both ; probably the answer 

 is in the affirmative. If it is so, we are faced with the following 

 possibilities : — 



A. — Sucrose is immediately concerned with the formation of the starch in 

 the lamellae, and the quantities of sucrose that find their way into the stem 

 are concerned solely with maintenance of the starch reserve there ; in the 

 last sentence the word "solely" must be emphasized, because the small 

 quantities that occur in the stem would only be adequate provided they 

 were entirely devoted to this work ; but that this is not so is shown by 

 the fact that invertase in large quantities occurs in the stem. It is further 

 questionable whether the amount of sucrose which penetrates the rhizome 

 would be adequate even if it was devoted exclusively to this work. It is 

 reasonable therefore to conclude that either maltose or a hexose is respon- 

 sible for the formation of starch. But maltose seems out of the question, 

 since it is not known to arise, except from the hydrolysis of starch, whereas 

 a constant supply from the leaves is necessary for this task. The only 

 sugars that come down from the leaves in quantities anything like sufficient 

 to maintain the starch supply are the hexoses. 



B. — If it be granted that the same sugar is concerned in the formation of 

 starch in both leaf and stem, then it follows that small quantities of sucrose 

 in the plastids of the lamellae must be inverted, and that this invert sugar or 

 one of its members must be responsible for the maintenance of starch in the 

 leaf lamellae. 



SUMMAET. 



1. Dextrose, levulose, and sucrose have been found in all the material 



examined, whereas maltose is dependent on the presence of starch. 



2. Invertase is of wide distribution, whereas diastase and maltase have 



been found in P. commune alone. Thus their detection is dependent 

 on the presence of appreciable quantities of starch. 



