132 Trans. Acad. Sci. of St. Louis. 



may serve the most diverse organic purpose, that sometimes 

 analagous organs, like the leaf of the moss and that of the 

 flowering plant, cannot be morphologically compared, since 

 they are parts of fundamentally unlike plant bodies, shown 

 primarily by Hofmeister's discovery of alternating genera- 

 tions in 1851 (one representing the gametophyte and the 

 other the sporophyte of beings with alternating sexual and 

 non-sexual generations), and that cells, cellular tissues, and 

 systems of such tissues show a similar and comparable plia- 

 bility in their adaptation to physiological function, as Haber- 

 land and others have made clearly evident, with many other 

 facts of equal importance for a right understanding of nature, 

 may be credited in large part to the last half, and, as to much 

 of their detail, to the last quarter, of the century. Indeed, 

 the consideration of tissues from a proper morphological 

 point of view dates practically from Han stein's studies in 

 1868, and their rational terminology was established by 

 DeBary nearly a decade later. 



Though initially wrong, Schleiden as early as 1837 laid the 

 foundation of embryology in botany, and the organogenetic 

 studies of Hofmeister, Payer, Sachs and Goebel will always 

 stand as classics in the application of the developmental line 

 of research to the progressively formed grosser parts of more 

 mature plants. 



PHYSIOLOGY. 



Physiology, either of animals or plants, could scarcely have 

 become a science before the determination of the grosser 

 chemical composition of the atmosphere, which, made by the 

 chemist Priestley toward the end of the Eighteenth Century, 

 was quickly followed up by him, Ingen-Housz, de Saussure, 

 Hales and numerous others, with the result of showing that 

 a very considerable part of the organic matter of which 

 plants consist is derived from the carbon dioxide of the at- 

 mosphere, which is fixed in carbohydrate form in the green 

 parts of plants under the influence of light ; and the studies 

 of Draper and Wilhelm Engelmann stand out in prominence 

 as contributing to our present knowledge that certain wave- 

 lengths of sunlight, when passing through the chlorophyll 

 or comparable pigments of plants, disappear as light, and are 



