1878.] 



President's Address. 



57 



If we call up in our mind's eye some vegetable organism and briefly 

 reflect on its construction, we see that we may fix on three great steps 

 in the analysis of its structure, the organic, the microscopic, and the 

 molecular, and, although not in the same order, each of the three last 

 centuries is identified with one of these. In the 17th century Grew 

 achieved the microscopic analysis of plant tissues into their constituent 

 cells ; in the 18th, Caspar Wolff effected the organic analysis (inde- 

 pendently but long subsequently expounded by the poet Goethe) of 

 plant structures into stem and leaf. It remained for Nageli in the 

 present century to first lift the veil from the mysterious processes of 

 plant growth, and by his memorable theory of the molecular constitu- 

 tion of the starch-grain and cell-wall, and their growth by intussus- 

 ception (1858), to bring a large class of vital phenomena within the 

 limits of physical interpretation. Strasburger has lately (1876) 

 followed Sachs in extending Nageli's views to the constitution of 

 protoplasm itself, and there is now reason to believe that the ultimate 

 structure of plants consists universally of solid molecules (not how- 

 ever identical with chemical molecules) surrounded with areas of 

 water which may be extended or diminished. While the molecules 

 of all the inert parts of plants (starch-grains, cell-wall, &c.) are on 

 optical grounds believed by most physiologists to have a definite 

 crystalline character, no such conclusion can be arrived at with 

 respect to the molecules of protoplasm. In these molecules the 

 characteristic properties of the protoplasm reside, and are more 

 marked in the aggregate mass in proportion to its denseness, and this 

 is due to the close approximation of the molecules and the tenuity of 

 their watery envelopes. The more voluminous the envelopes, the more 

 the properties of protoplasm merge in those of all other fluids. 



It is, however, to the study of the nuclei of cells that attention has 

 been recently paid with the most interesting results. These well- 

 known structures, first observed by Ferdinand Bauer at the beginning 

 of the century (1802), were only accurately described thirty years 

 later by Robert Brown (1833). Up to the present time their 

 function has been extremely obscure. The beautiful investigations 

 of Strasburger (1875) have led him to the conclusion that the 

 nucleus is the seat of a central force which has a kind of polarising 

 influence upon the protoplasm molecules, causing them to arrange 

 themselves in lines radiating outwards. Cell-division he regards as 

 primarily caused by the nucleus becoming bipolar, and the so-called 

 caryolitic figures first described by Auerbach, exhibit the same 

 arrangement of the protoplasm molecules in connecting curves as in 

 the case of iron-filings about the two poles of a bar-magnet. The two 

 new centres mutually retire, and each influencing its own tract of 

 protoplasm, the cell-division is thereby ultimately effected. This is 

 but a brief account of processes which are greatly complicated in 



