154 The Mode of Examining the [TCJM^iym. 



9. U. tumidum, sp. nov. (Plate XLIII., Figs. 5-7). Cicatrices 

 small, oval, eight lines long by six lines broad, borne on tumid 

 swellings on the opposite sides of the stem ; solitary cicatrices scat- 

 tered over the stem; scar of the compact bundle circular, of the 

 separate bundles pit-hke ; few in number ; leaves with a broad base 

 imbricated. 



Fig. 5 represents a portion of the specimen one-third the natural 

 size ; it has lost all indications of the bases of the leaves, except on 

 one or two patches, one of which, from the surface not shown in the 

 figure, is represented natural size at Fig. 6 ; and one of the cica- 

 trices, natural size, in Fig. 7. 



From the Coal-measures. Britain — locality unknown. [British 

 jMuseum.] 



IV. — The Mode of Examining the Microscopic Structure of 

 Plants. By W. E. M'Nab, M.D. Edin. 



IT. 



Having now considered the Cell-wall, we have next to take up the 

 subject of the Protoplasm, Nucleus, and Cell-sap. The Protoplasm 

 is a mixture of albuminous materials with water, and a small 

 quantity of incombustible matter. In the young and active state 

 of the cell, the whole of the cavity is filled u]3 with the protoplasm. 

 Mixed with the protoplasm we have various organic materials, as 

 oils, starch, &c., which often increase to a very great extent, or else 

 disappear altogether, leaving the cell-wall empty. The quantity of 

 water in the protoplasm seems to vary, and as a consequence we 

 find that the consistence of the protoplasm also varies, being some- 

 times very fluid. Imbedded in the protoplasm, and always in rela- 

 tion to it, we find the more solid protoplasmic body, the nucleus. 

 The presence of a nucleus is not constant, as we sometimes have 

 cells without one, either the cells never having formed one, or the 

 nucleus after having been formed being dissolved in the general 

 mass of protoplasm, and thus disappearing. In Chara we find that 

 as the circulation in the cells begins the nucleus disappears. Besides 

 forming the nucleus, the protoplasm seems intimately connectal with 

 the formation of chlorophyll and starch. The protoplasm is cajDable 

 at certain times of moving. These movements are either slow or 

 rapid, and three distinct kinds of movements have been described. 

 In the remarkable conditions of that peculiar group of Fungi, the 

 Myxomycetes, we have the external form of the masses of protoplasm 

 constantly changing. Again, in some zoospores we find that the 

 whole mass of protoplasm moves freely about by means of the 



