1883.] on the Swelling of Starch Grains. 405 



of the structure of the starch grain. Divesting ourselves of all bias 

 derived from pre-conceived notions in favour of one or another of 

 the theories which have been promulgated, what are the simple 

 conclusions which we should derive from a consideration of evi- 

 dence such as the above ? They appear to me to be these : — That 

 a starch grain is composed of a series of (in a broad sense) concen- 

 tric layers, each bounded externally by a "limiting membrane" 

 of the same substance as the rest of the grain, soluble in the same 

 reagent, but often differing in its physical property of greater re- 

 sistance, and that the outermost layer of the grain is bounded 

 exteriorily by the most resistant of all these limiting membranes. 



If our attention were drawn to a starch grain in its perfect 

 state, and we saw the series of lines which pass around the excen- 

 trically placed centre of the grain, we should not, I think, hesitate 

 much in saying that, if those lines mean anything at all in the 

 anatomical structure of the grain, they have some relations to the 

 lamination shewn above to exist in the swollen grain. But, count- 

 ing the number of these lines existing in the starch grain, and 

 comparing it with that of the laminae in the swollen grain, a great 

 disparity will be seen generally to exist. The latter are outnum- 

 bered two or three or more to one. Return to the starch grain, 

 and it is seen that some of the lines are very delicate, while others 

 are strongly marked, and indeed, if the grain be at all " fresh," 

 these latter will be the only ones visible. Hence we should pro- 

 bably say that in the action of the reagent the delicate layers, (and 

 in some cases all the layers) are, as it were, merged, and that the 

 envelopes in the swollen grain correspond with the groups of layers 

 in the grain itself, or, to introduce here the terminology of Stras- 

 burger 1 , correspond with the "sheaths" (Schichten) or "complexes 

 of lamellae " {Lamellen-complexe) of the unswollen grain, and not 

 with the primary layers, or lamella? ; and that what I have here 

 described as the " limiting membrane " of the envelope corresponds 

 with the " Grenzhautchen " hypothecated by the same author in 

 the modern revival of the old theory of growth by apposition. It 

 must however be noted that Strasburger applies this word to what 

 he calls the denser inner edge of a complex of lamellae, while I 

 apply " limiting membrane " to the denser outer layer of a sheath, 

 for such I take it to be. 



The theory of growth by apposition alone appears to me capable 

 of explaining these phenomena in the swelling of starch grains, 

 phenomena which are quite inconsistent with the Nagelian theory 

 of the physico-anatomical structure of the grain. The " limiting 

 membrane" probably arises from a physical change which has 

 taken place in the outer part of the grain during a temporary halt 



1 Ueber den Bau unci das Wachsthum der Zellhaute, 1882, S. 6. 



