910 SUMMARY OF CURRENT RESEARCHES RELATING TO 



This structure was observed by Scbimper in tbe starcb-grains of 

 the cotyledons of Dolichos Lablab, the seeds of ViciaFaha and Phaseolus, 

 and the meduUary parenchyma of Cereus speciosissimus. 



It follows that the theory of Naegeli is incorrect, that the centre of 

 a starch-grain is the oldest part ; growth, on the contrary, takes place 

 by exogenous stratification. 



The course of development of a starch-grain is as follows : — 1. Its 

 first appearance in the form of a strongly refractive dense body, but 

 not, as Naegeli states, always spherical. 2. Differentiation of the 

 originally homogeneous grain into a central watery nucleus, and a 

 dense peripheral layer. 3. The formation of three layers, of which 

 the central one is always watery, surrounding the grain. 4. Increase 

 in the number of layers, the outermost being always dense. 5. In- 

 crease in the amount of water in the centre with the increase in size 

 of the grain. 



When starch- grains swell up in water, the deposition of water is, 

 as Naegeli was the first to point out, not equal in all directions, but 

 much greater in a direction parallel to the stratification than at right 

 angles to it. The contrary is, however, sometimes the case with 

 compound grains. 



Starch-grains differ from ordinary sphero-crystals in their capacity 

 for swelling ; the fibrous crystals which compose them must, there- 

 fore, be regarded as crystalloids, which term includes all crystalline 

 bodies capable of swelling. The investigations of the author show 

 that starch-grains consist of radially disposed crystalloids, present- 

 ing the crystallization of the starch-substances CeHjoOs, of which 

 there are jirobably several isomeric. Several circumstances combine 

 to show that the starch -crystalloids always occur in the form of fibrous 

 aggregates, never singly. 



Structure of Stomata.* — A. Tschirsch distinguishes two kinds 

 of stomata, which he terms the angiospermal and the arcJiegonial type. 

 The first of these is characterized by the outer and inner border of 

 the cuticle being developed, the outer one being usually considerably 

 thickened. In this way is produced the well-known form which 

 occurs in nearly all angiosperms, with an anterior and posterior 

 border, the eisodial (Verhofsausgangoffnung), and the opisthelial pore 

 (Hinterliofsausgangoffnung), and a central fissure. The second type 

 is characterized by the outer wall of the guard-cells being very much 

 thickened, while the inner wall usually consists of only a thin lamella, 

 and by the guard-cells being considerably sejjarated in their central 

 part, but not at the poles. The outer border of the cuticle is not 

 developed into a ridge, but is rounded off; while the inner one is 

 usually altogether wanting. It follows that there is never a posterior 

 border, and only occasionally an anterior border, as in some conifers. 

 The central fissure then opens directly into the subjacent cavity. 

 This kind occurs in archisperms (gymnosperms), and in vascular 

 cryptogams. Gymnosperms are, therefore, as regards the structure of 



* Verhandl. Bot. Ver. Prov. Brandenburg, 1880, p. 116. See Bot. Centralbl, 

 vi. (1881) p. 341. 



