REVIEWS. 409 



alteration due to the environment, and it is important to 

 notice that this hiyer — of the nature of a " limiting mem- 

 brane " — is in part formed where the edges of incomplete 

 starch layers overlap. 



Strasburger declares that the most resistant part of the 

 starch grain is that which has been longest subjected to the 

 action of the environment; the inner parts vary according to 

 circumstances. By the careful use of reagents, observations 

 on the process of swelling, &c., it is possible to demonstrate 

 radial structure in the separate layers^ and a correspondence 

 between the tangential and radial structure is traced similar 

 to what was obtained for the wood-cells in Pmus, &c. 

 Naegeli's explanation of the markings and structure of the 

 starch grain is found to be insufficient, and after examining 

 the facts derived from observations on other starch grains^ 

 especially those of Cycas, Phaseolus, Potato, «&c. — Strasburger 

 proceeds to another explanation of these and other similar 

 phenomena. Some ten pages are occupied with his views 

 " Ueber den Bau der Stcirkekdrner und Zellhdute, und das 

 Verhdltiiiss der QuellungsricJitungen zu dem anatomischen 

 Bau." 



Strasburger agrees with Schleiden, Unger, Cruger, 

 Schacht, and Schimper, &c., that the starch grain grows by 

 apposition of new layers. Schimper had already shown 

 that new layers can be formed over the nucleus of a cor- 

 roded grain ; but explained them otherwise than by simple 

 apposition, attempting, in fact, to reconcile Naegeli's views 

 as to the alternation of watery and less watery strata with 

 his own views of deposition. The ingenious explanation of 

 the layers in the starch grain offered lately by Arthur 

 Meyer, does not appear to us fully dealt with by Stras- 

 burger. The views held by the latter may be fairly sum- 

 marised as follows. 



The central " nucleus " of the starch grain is soft. In 

 general any layer after being covered by another becomes 

 less refractive, depending on its assumption of water ; in 

 this manner is explained the fact that the layers become 

 softer and less refractive as they approach the centre of the 

 grain. Those layers which do not become covered by others 

 preserve their density, or become denser ; in this way the 

 darker lines become formed during pauses in the growth of 

 the grain. 



Since each new lamella is closely and tightly affixed on 

 those beneath, a strain is produced on the former as the 

 latter becomes more watery, and the tendency of the latter 

 to absorb water is favoured by the strains in the starch 



