of the Wall and Connecting Threads in the Plant Cell. 187 



communis ; (h) in part continued, and in part overlaid by superposed 

 lamellae of cellulose membrane, e.g., the endosperm cells of Lilium 

 Maria gon ; or, (c) all overlaid, e.g., the pollen mother-cells and pollen 

 grains of Eellebm-us foetidus. 



2. Origin and Development of the Cell Wall. 



(a) Origin. — Seeing that spindle fibre nodes (apparently intact) can 

 be recognised in a mature wall of considerable thickness, there would 

 seem little doubt that the existing views with regard to the genesis of 

 the cell plate and first formed cell wall cannot be entirely correct. 



I am inclined to believe that the cell plate arises not directly from 

 the spindle fibres, in the manner described by Strasburger and others, 

 but rather indirectly; that is to say, that although it is possibly pro- 

 vided by or even proceeds from the fibres in question, yet it exhibits a 

 certain structural distinction, in that it is pierced by the persistent 

 nodes of the spindle fibres, and is not merged into their substance. 



The cell plate would appear to consist of cytoplasm, and cytoplasm, 

 moreover, practically identical with the ordinary cytoplasm of the cell, 

 and from it is secreted the first formed cell wall as an equatorial mem- 

 brane traversed by the nodes of the achromatin spindle fibres. 



(b) Development. — There are grounds for regarding the primary cell 

 wall as different in genesis and character from the secondary formations 

 which succeed it and arise from the general cytoplasm. In any case, 

 the wall rapidly grows in thickness as layer after layer of cellulose is 

 deposited. In the course of my work certain observations were made, 

 which appeared to throw some light on the structure and genesis of 

 the wall thus produced. It was found that many walls, and especially 

 mucilaginous walls, when strongly swollen and stained, after passing 

 through the stage of stratification, became resolved into numberless and 

 often well-defined spherical droplets or spherules which not unf requently 

 exhibit a markedly high refraction, and are embedded in a hyaline and 

 possibly mucilaginous ground-substance or matrix. 



I am of opinion that these spheroidal droplets represent swollen 

 granules or spherules, which are practically homologous with the 

 droplets or the drops (and I am disposed to think with the droplets) 

 described by myself and Ito in our paper " On the Structure of the 

 Mucilage-secreting Cells of Blechnum occidentale, L., and Osmunda regalis, 

 L.," published in 1887 in the August number of the 'Annals of 

 Botany ' ; and I believe that the phenomena in the two cases of internal 

 mucilage there described, were in essence, instances of internal wall 

 formation, or, in other words, that the formation of the cell wall 

 takes place in a similar way. Moreover, the " mucilage " described by 

 us, both gave the reactions of cellulose, and also exhibited the forma- 

 tion of a firm, clear, and stratified membrane. 



