118 THE DATA OF BIOLOGY. 



nary vegetal cell forming part of a leaf or other plant- 

 structure. Its limiting membrane, originally made poly- 

 hedral by pressure of adjacent cells, is gradually moulded 

 "into one of cylindrical, fibrous, or tabular shape, and 

 strengthening its walls with pilasters, borders, ridges, hooks, 

 bands, and panels of various kinds'' (Kerner, i, 43) : small 

 openings into adjacent cells being either left or subsequently 

 made. Consisting of non-nitrogenous, inactive matters, 

 these structures are formed by the inclosed protoplast. How 

 formed? Is it by the agency of the nucleus? But the 

 nucleus, even had it characters conceivably adapting it to 

 this function, is irregularly placed; and that it should work 

 the same effects upon the cell-wall whether seated in the 

 middle, at one end, or one side, is incomprehensible. Is the 

 protoplasm then the active agent ? But this is arranged into 

 a network of strands and threads utterly irregular in distri- 

 bution and perpetually altering their shapes and connexions. 

 Exercise of fit directive action by the protoplasm is un- 

 imaginable. 



Another instance : — Consider the reproductive changes ex- 

 hibited by the Spirogyra. The delicate threads which, in 

 this low type of Alga, are constituted of single elongated 

 cells joined end to end, are here and there adjacent to one 

 another; and from a cell of one thread and a cell of another 

 at fit distance, grow out prominences which, meeting in the 

 interspace and forming a channel by the dissolution of their 

 adjoined cell- walls, empty through it the endochrome of the 

 one cell into the other : forming by fusion of the two a zygote 

 or reproductive body. Under what influence is this action 

 initiated and guided? There is no conceivable directive 

 agency in either cell by which, when conditions are fit, a 

 papilla is so formed as to meet an opposite papilla. 



Or again, contemplate the still more marvellous trans- 

 formation occurring in Ilydrodictyon utriculosum. United 

 with others to form a cylindrical network, each sausage- 

 shaped cell of this Alga contains, when fully developed, a 



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