384 HOPMEISTER, ON 



organ becomes farther developed, are thrown off with the 

 cells which bear them. The adventitious roots of the larger 

 species fork frequently even long before they reach the 

 ground. Those of S. hortensis usually ramify for the first 

 time after they have penetrated into the ground. The 

 foundation for the first ramification is however here also 

 laid at an earlier period. The aerial roots as soon as they 

 have reached a certain stage of development exhibit a 

 spherical enlargement of the end. # This thickening of the 

 tip of the root is formed by the commencement of furcation : 

 the lenticular cell of the first degree of the root has divided 

 by a longitudinal septum into halves, each of which com- 

 mences an independent multiplication in a direction away 

 from the other. The two rudimentary branches thus formed, 

 surrounded by the outer cellular layers of the root, which 

 were formed before the commencement of the forking, con- 

 stitute the almost spherical mass of the end of the root. 



It is a known fact that the smallest fragment of the stem 

 of Selaginella when properly treated — that is, kept moist 

 and warm upon loose earth — will produce a new plant. 

 This depends upon the production of adventitious roots in 

 definite positions : in the angles formed by the vascular 

 bundles which branch off into the leaves with the vascular 

 bundles of the stem. The adventitious shoot breaks through 

 the cortical layer of the stem and is developed into a new 

 plant by a succession of shoots, in the same manner as 

 an embryo is produced by impregnation of an archeog- 

 nium, after an adventitious root has grown out close to its 

 place of origin (PL LVI, fig. 10). 



Fruit is formed in Selaginella only on particular shoots 

 differing greatly in their habit from the vegetative shoots. 

 The branch destined to develope sporangia is, like the 

 vegetative branches, a fork of the naked end of the shoot 

 of the preceding order. It is distinguished from the vege- 

 tative shoots even in its earliest condition by a far less rapid 

 increase in length, so that, even in Selaginella denticulata, 

 it is soon pushed to the side of the vegetative shoot — whose 

 direction is the same as that of the shoot of the preceding 

 order — and might be taken for an immediate prolongation 



* Kaulfuss, Wesen der Farrnkrauter, 5 p. 64. 



