8 ANATOMY AND PnYSIOLOGY OF 



tliem, especially Hayne {^' FIoqxo''' 1827, ii. QOl^Mejen ('' Fhytotomie'' 57, 

 " Phjsiologie'' i, 12), and Morren {^^ Bulletin de VAcad deJBruxelles" V, J!^o, 3). 

 The arrangement of Hayne, wMcli did not attract tlie least notice, I may 

 pass over here. Mey en distinguished: \, Mere^icliyma — tissue composed 

 of spherical cells, the cells only i^artially in contact ; 2, Parenchyma; 3, 

 Frosenchyma — ^this name was applied by Meyen to the woody tissue of the 

 Coniferse ; 4, Fleurenchyma, which was the name by which he distin- 

 guibhed the prosenchyma of all other plants. The division of merenchyma 

 from parenchyma was superfluous, and cannot be carried out, because there 

 are so many transitional forms ; the alteration of the established term 

 prosenchyma into pleurenchyma was altogether inconvenient, and was not 

 adopted. But the wilderness of botanical terminology would have been 

 increased beyond all reasonable measure by Morren, had not his subdivi- 

 sions been passed over unregarded ; for he divided the parench3?Tna alone 

 into no IckSs than eight tissues, which he named, merenchyma^ conenchyma, 

 onenchyma, atractenchyma, cylindrenchyma, colpenchyma, cladenchyma, 

 and j9r'i*s?>^e^^c/My??^o^. AH such far-fetched subdivisions of the cellular 

 tissue are wholly valueless, because no exact connexion exists between 

 form and function, and frequently enough the same organ is formed of 

 cells differing considerably in form, — ^in two closely allied plants. 



B. SIZE OF THE CELL. 



Important as the accurate determination of the size of the indi- 

 vidual elementary organ is, in many special researches, particularly 

 those relating to the history of development, yet in general the 

 knowledge of the size of cells is of very subordinate value ; and 

 this the more that not only do the cells of the same organ exhibit 

 extraordinarily great variations in respect to their size, but the 

 contiguous cells of one and the same organ not unfrequently differ 

 considerably from each other. Pollen grains afford a very striking 

 example of the former ; their dimensions are tolerably constant in 

 each species of plant ; but their diameter varies from 1-3 00th of a 

 line in Myosoiis to 1-1 5th of aline and more in Ciicurbita, Sire- 

 litcia, (ic. The cells of a single organ often dijBfer to the extent of 

 some being twice or thrice as large as others. 



The diameter of the cells of parenchyma may be stated at a 

 general average of from l-20th to 1-lOOth of a line ; but in paiti- 

 cular cases (e. g , in the spores of many Fungi, in the yeast cells) it 

 fells to less than l-500th, and in other instances it rises, 6. ^., in 

 succulent parts, in the pith of the elder, &c,, to 1-1 0th of a line and 

 more ; so that in such cases the individual cells are actually visible 

 to the naked eye, which is not generally the case. 



The dimensions of many elongated cells form a striking contrast 

 with this small magnitude of the majority of parenchymatous cells, 

 since while the transverse diameter of the former is usually consi- 

 derably smaller than the diameter of the parenchymatous cells, 

 the longitudinal extension is very remarkable. In regard to the 

 majority of elongated cells, especially the prosenchymatous cells of 

 the wood and hast or liber of most plants, we should be very much 



