THE HIGHER CRYPTOGAMIA. 379 



Selasjinella terminates Ions; before that of the leaf to which 

 it belongs. It is only to be found in full vitality amongst 

 the closely crowded leaves of the bud ; in the axils of 

 those leaves between which the last longitudinal expansion 

 of the stem began it is always shrivelled and inconspicuous. 

 Spring, who has written a monograph of the family, has 

 not himself seen the organ. 



That region of the young leaf which, by repeated division 

 parallel to the surface of the cells of the underside, becomes 

 transformed into the mid-rib, corresponds exactly in breadth 

 with the place of attachment of the leaf. This breadth in 

 the youngest state of the leaf, and up to the time when the 

 formation of the mid-rib begins, is equal to one fourth part 

 of the circumference of the stem. It is afterwards much 

 less, inasmuch as after the commencement of the formation 

 of the leaf the number of the cells of the circumference 

 of the stem continues to increase. Each of the transverse 

 rows of cells of the circumference of the stem — by whose 

 multiplication a leaf is produced belonging to one of the 

 four longitudinal rows in which the leaves of the greater 

 number of the species of Selaginella are arranged — stands 

 immediately above the place of insertion of the next lower 

 leaf (PL LV, figs. 11, 12). The circumference of the stem 

 becomes thickened as in the Equisetaceae by the growth in 

 thickness of the bases of the leaves, which originate close above 

 each other, and by the often repeated division, parallel 

 to the longitudinal axis of the leaf, of the cells of the base 

 of its under-side. Its periphery appears to be formed of a 

 number of cellular layers produced by the multiplication of 

 the cells of the young rudiment of the leaf (PI. LV, 

 fig. 11). The axile cells of the stem which correspond 

 with the naked end of the bud — which naked end projects 

 above the rudiment of the youngest leaf — enter for the 

 most part into the formation of the vascular bundles and 

 the parenchyma between them. 



When the leaf is almost fully formed every other one of 

 its marginal cells expands laterally into a blunt papilla, 

 whih becomes rapidly elongated, often to a very consider - 

 able extent, as for instance at the base of the upper leaves* 



* The " Intermediaren Blatter " of Spring. 



