908 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Formation and Growth of the Cell-wall.* — F. Schmitz argues in 

 favour of the older theory of apposition as opposed to that of intussus- 

 ception, in the increase in thickness of the cell-wall. He maintains 

 that cellulose is not formed by secretion, but by metamorphosis out of 

 the protoplasm. This he deduces not only from the processes in 

 those cells which finally become empty, but also from the gradual 

 transformation of the protoplasm into a parietal layer, and from the 

 phenomena that accompany the increase in thickness of the cell-wall. 

 The outermost layer of the protoplasm gradually developes into a 

 stratum constantly increasing in thickness, which is at first still 

 firmly united to the rest of the protoplasm, but which gradually 

 becomes separated from it, and finally adheres to the cell-wall as its 

 innermost thickening-layer, as has already been described by Prings- 

 heim. The formation of partial secondary deposits also takes place, 

 according to the author, by metamorphosis from the protoplasm. In 

 cells of the testa of the seed of Torenia Fournieri, which show a 

 thick thickening-baud on the two opposite sides, the primordial 

 utricle first of all becomes thicker at these places, a number of 

 granules accumulating in them ; a string of a denser substance is 

 then formed at these spots in the superficial layer of the primordial 

 utricle ; and this finally becomes the thickening-band. 



When a cell divides, a single layer of granules, Schmitz's " micro- 

 somes," first collects at the spot where the new wall is formed ; this 

 then extends along the wall of the mother-cell, and is finally trans- 

 formed into the young cell-wall of the daughter-cells by the coales- 

 cence of the microsomes and chemical transformation of their sub- 

 stance. Schmitz, however, admits that the protoplasmic disk which 

 bears these microsomes, probably itself becomes the cell-wall by 

 absorption of the substance of the microsomes. Even in those Algas, 

 as Cladophora, Conferva, and Spirogyra, in which the division-wall is 

 formed gradually, it arises from the protoplasm, a protoplasmic 

 division-wall being gradually developed in the form of an annular 

 disk which becomes constantly narrower, and is finally transformed 

 into cellulose. 



Although the author considers he has proved the growth of the 

 cell-wall by apposition, he is inclined to believe that the intussus- 

 ception theory may be true in some instances. Even in the cases of 

 a so-called centrifugal increase in thickness of the cell-wall, as in the 

 formation of the cuticle of pollen-grains, in the only case examined by 

 Schmitz, that of Cobcea scandens, a centripetal process of apposition is 

 possible, since the outermost layer, with its spines and bands, is formed 

 earlier than the cell-wall of the pollen-grain. 



Even in the superficial growth of the cell-wall as the cell increases 

 in size, the author considers the intussusception theory not proved, since 

 in many cases a stratification may be observed. The outer older lamellaj 

 of the cell-wall are only momentarily stretched passively, and either 

 remain permanently in the form of a general envelope, as in Cladophora, 

 or are thrown off in various ways, as in Holosphcera and Glosocapsa. In 



* SB. niederrhein. Ges. f. Natur- u. Heilkunde, Bonn, Dec. 6, 1880. See Bot. 

 Centralbl., vi. (1881}p. 187. 



