THE CELL. 19 



forces " lohose nature is unhiown.'''' ' Nilgeli has probably ad- 

 vanced as far as it is possible to go in this field of investigation. He 

 has reached the given forces inherent in the smallest particles of 

 matter. 



The above does not compel us to accept the intussusception 

 theory. However, it cannot be denied that the evidence given 

 explains certain phenomena more satisfactorily than the apposition 

 theory. 



It would be very desirable to establish a definite reliable life- 

 bistory of a starch-grain ; to observe directly its development from 

 beginning to end, for example in a culture medium. We arrive at 

 the conclusion of ''younger" and "older" stages of starch develop- 

 ment in an abstract way by describing as many stages or condi- 

 tions as we happen to observe. Conclusions as to age are then in- 

 directly reached according to the size of the starch-grain under 

 examination and by other considerations. 



The opinion of Akthur Meyer * that stratification of starch- 

 grains is the result of fermentation (dissolving effect) combined with 

 periodic apposition is opposed by Krabbe, ^ according to whose 

 investigations diastase, i\\Q starch-dissolving ferment, always acts on 

 the exterior and never enters the starch-substance no matter how 

 deep or variable the corrosions may appear. It must be observed 

 that this corrosion as the result of solution by means of diastase 

 is still an unexplained phenomenon. 



The following statements will assist in explaining the minute 

 structure of starch-grains. When a fresh starch-grain becomes dry 

 crevices are formed in a radial direction at right angles to the strati- 

 fications. In the interior where the split begins there is a hollow 

 space ; the crevices become narrower outward. The fact that the 

 greatest loss of water is in the interior and in the radial directions 

 of the crevices indicates (1) that the entire starch-grain contains 

 gradually more water from without inward, and (2) that in every 

 layer or stratum the deposition of water-molecules is more activ^e 

 in the tangential direction than in the radial, since cohesion is less 

 in the tangential direction. 



Chemical Properties and Solution of Starch-grains. — To test 

 the presence of starch microscopically we resort to one of the few 



1 Starkekorner, p. 332. 



''Botanische Zeitung, 1881. 



* Pringsheim's Jabrbiicber, 1890. 



