68 NOTES AND MEMORANDA. 



make any substantial addition to the labours of Grew and Malpighi 

 for more tban a century and a half, and however remarkable is the 

 impulse which he gave to morphological studies, the views of Caspar 

 Woltf in the middle of the eighteenth century (1759), in regarding 

 cells as the result of the action of an organizing power upon a matrix, 

 and not as themselves influencing organization, were adverse to the 

 progress of histology. It is from Schleiden (1838), who described 

 the cell as the true unit of vegetable structure, and Schwann, who 

 extended this view to all organisms whether plants or animals, and 

 gave its modern basis to biology by reasserting the unity of organiza- 

 tion throughout animated nature, that we must date the modern 

 achievements of histological science. Seldom, perhaps, in the history 

 of science has any one man been allowed to see so magnificent a 

 development of his ideas in the space of his own lifetime as has 

 slowly grown up before the eyes of the venerable Schwann, and it 

 was therefore with jjeculiar pleasure that a letter of congratulation 

 was entrusted by the officers to one of the Fellows of this Society on 

 its behalf on the recent occasion of the celebration of the fortieth 

 anniversary of Schwann's entry into the professoriate. 



If we can 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 micro- 

 scopic, and the molecular, and, although not in the same order, each 

 of the three last centuries is identified with one of these. In the 

 seventeenth century Grew achieved the microscopic analysis of plant 

 tissues into their constituent cells ; in the eighteenth, Caspar Wolff 

 effected the organic analysis (independently but long subsequently ex 

 pounded 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 constitution of the starch-grain and cell-wall, 

 and their growth by intus-susception (1858), to bring a large class of 

 vital phenomena within the limits of physical interpretation. Stras- 

 burger has lately (1876) followed Sachs in extending Nageli's views 

 to the constitution of protojolasm itself, and there is now reason to 

 believe that the ultimate structure of plants consists universally of 

 solid molecules (not however, identical with chemical molecules) sur- 

 rounded 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 to have a definite 

 crystalline character, no such conclusion can be arrived at with 

 respect to the molecules of protoplasm. In tliese 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 



