154 THE PHENOMENON OF 



stem, starting from uniform* or dissimilarf division in 

 the link-cells ; how, moreover, the vessels are formed in 

 the parenchyma of the stem in the vascular plants, i. e., 

 how their origin is connected with the generative suc- 

 cession of the rest of the cells. J It must likewise be 

 demonstrated how the cell- formation in the leaf, pro- 

 gressing according to fixed laws, produces the simple 

 cellular plate, such as is exhibited by most Mosses, and 

 the many-layered plate, with varied arrangement and 

 direction of the cells in the different layers, of the higher 

 plants ; how here again the formation of the vascular 

 bundles enters into the tissue in the most diverse dis- 

 tribution, and how these vascular bundles are connected 

 in their origin with those of the stem. Finally, it must 

 be demonstrated how, beyond all the generations of 

 cells arriving at vegetative permanence and at their final 

 term in the graduated construction of the organism and 

 the contrast of its organs, certain series of generations, 

 withdrawing themselves from the vegetative termination, 

 finally attain their destination prepared, protected, and 

 supported by all the other series, in the formation of 

 reproductive cells. 



We have here stated a problem, the solution of which 



* Vide Slyptocaidon, iiiKiitziiig's 'Piiyool. generalis,' t. xviii; in Lemania 

 also, the formation of tli(! oompoiiad tissue starts from a simple row of link- 

 cells originating by horizontal division of an apical cell, which link-cells 

 divide first by a cross-wise perpendicular segmentation into four, then by 

 recurring horizontal division into eight equal cells. In what way the 

 separation in the peripherical and central cells next takes place, and how the 

 division proceeds in the interior, it is not easy to determine ; but the result 

 shows that the division occurring in the interior is far outstripped by tliat 

 in the peripherical cells, since a rind is formed outside composed of two 

 layers of very small cells, while the interior is occupied by many-times larger 

 cells, separating from one another in the centre, and forming a medullary 

 cavity. 



t Vide Plilohi (Kiitz. ' Phyc. general.,' t. '10, vi) ; Naecaria (ibid., t. 44, 

 iv) ; AhhJiiim Helminthochorton (ibid., t. 45, xi) ; Laurenria (Niigeli, 

 ' Algensyst.,' t. 8). 



X Unger's treatise on the ' Genesis of Spiral Vessels' (Linnsea, 1841, 

 3S5, t. 5) shows that the so-called vessels of jilauts are only rows of cells of 

 |)cciiliar kind. (Transl. in 'Ann. dcs Sc. nat.,' 2d ser., t. xvii, p. iiV,. See 

 also Muhl, 'A'crm. Schriftcii,' 2sl; Sohaclit, ' rflanzcnzelle,' 1-S5.— A. H.) 



