NOTES AND MEMORANDA. 317 



Homology of the "Nucule" of Characeae. — The female organ 

 of Charaeese, variously termed nucule, oogonium, and archegonium, 

 has been treated by A. Braun, Sachs, and others, as a metamor- 

 phosed shoot ; whence the ordinary German appellation of " Sporen- 

 sprosschen." In ' Flora' * Celakovsky gives reasons for regarding the 

 enclosed (behiillte) oogonium, as he prefers to call it, as homologous 

 morphologically with the globule or male organ, viz. a metamorphosed 

 foliar structure or portion of a leaf, and consequently homologous 

 also with the ovule of flowering plants. 



Arrangement of the Cells in the flat Prothallia of Ferns. — In 

 a series of observations on this subject, j Dr. Prantl states that the first 

 divisions which convert a filament into a plate of cells are not deter- 

 mined by its position with respect to light nor with respect to 

 gravitation ; the subsequent position of the plate at right angles to the 

 incident light being the result of torsion. In those prothallia which 

 possess a meristem, its cells are distinguished by their smaller size, 

 denser protoplasm, and more frequent division ; these prothallia, 

 therefore, grow more rapidly than those that are ameristic. The 

 absence of meristem is generally the result of a deficiency either of 

 light or of water. Archegonia are formed especially in the neighbour- 

 hood of a meristem, from cells which have just been produced from 

 the meristem, and therefore usually arise in acropetal succession. The 

 absence of archegonia is generally due to the want of meristem. The 

 antheridia of ferns are, on the other hand, trichomes, and may spring 

 from any of the older cells, and may consequently occur on ameristic 

 prothallia. Prantl completely confirms Sachs's statement that the new 

 division-wall is always nearly vertical to that from which it springs ; 

 and this is even the case in the wedge-shaped apical cell. 



The position and extent of the meristem vary in difierent pro- 

 thallia. In some it occupies the larger part or even the whole of the 

 free margin, and may then be termed marginal meristem. In others it 

 occupies only a small portion of the margin near the apex, and is then 

 an apical meristem. This meristem passes gradually into permanent 

 tissue, there being no sharp line of demarcation between them. A 

 single cell of the apical meristem which possesses the merismatic pro- 

 perty in excess, and every division of which helps to form the curve 

 of the margin, is known as the apical cell ; but it is often a matter of 

 great difficulty to distinguish the apical cell from its neighbours. The 

 absolute increase of the cells Prantl found to be less, the smaller the 

 size of the cells, and consequently least in the meristem ; while the 

 increase in proportion to the size of the cell is greatest in the 

 meristem, and sometimes gi'eatest of all in the apical cell itself. 



Apogamous Ferns and the Phenomenon of Apogamy in general. 

 — Professor A. De Bary, in an article bearing the above title, in the 

 ' Botanische Zeitung,' | gives the results of his observations on non- 

 sexual reproduction in ferns as first described in 1874 by Dr. Farlow. 



* ' Flora,' xxxvi. (1878) p. 49 et sea. 



t Ibid., 497. 



t July 19th, 1878, et seq. 



