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tions and markings. Strasburgev finds that the thin layer of 

 protoplasm lining the cell-wall, and applied to its inner 

 layers, carries numerous " microsomes/' which become used 

 up as growth proceeds ; that these " microsomes" are arranged 

 in corresponding directions with the spirals, &c., and that 

 in alcohol the contracted protoplasm may break up into 

 spiral bands corresponding to series of the granules. He 

 also finds that according to the stage of apposition the 

 " microsome " bearing sheet can or cannot be withdrawn 

 from the cell-wall. At last alcohol does not cause with- 

 drawal of the protoplasm, and no more " microsomes " can be 

 seen ; they have all been deposited in successive "lamellae " 

 to form the thickening layers. 



The persistence of the nucleus in these wood-cells till the 

 last may be noted. Many details as to the micro-chemical 

 reactions, &c., must be here passed over. It is important 

 that in the cross-section only concentric lines (the layers and 

 lamellse) are detected when no spiral strire occur in the 

 longitudinal surface view. When striae occur the concentric 

 lamellffi in the cross-section are traversed by radial striae, 

 giving the appearance as if the lamellae were made up of 

 rodlets. Where coarse and fine striations coexist in the longi- 

 tudinal sections the cross-section shows corresponding broad 

 and narrow markings. All these indications of structure 

 pass into one another by every gradation, and are in. accord 

 with corresponding arrangements of the " microsomes,'^ 

 whence must follow that they depend upon the mode of 

 building up of the "lamellae" out of the sheets of "micro- 

 somes" brought by the protoplasm. 



Reference only can here be made regarding the further 

 observations on the striation and lamellation of ordinary 

 cell'Walls. Some important observations on Spirogyra and 

 Cladophora follow the examination of schlerenchyma fibres, 

 &c., while the epidermis cells and vessels of many difi'erent 

 examples afford still further support to Professor Stras- 

 burger's view. If the description and figure relating to 

 the perfect agreement of the striae and " microsomes " on 

 the vessels of Impatiens are correct a better demonstration 

 could scarcely be desired. 



In that portion of the book dealing with the development 

 of the pollen grains of the Angiosperms and Gymnosperms 

 we need only select one example to illustrate the character 

 and importance of the facts adduced. 



In the Malvacea Strasburger finds that the pollen mother- 

 cells, after dividing into groups of four, begin to disappear; 

 their walls and those of the tetrads become swollen and 



