386 HOFMEISTEU, ON 



even the fifth-youngest sporangia have the appearance of a 

 central group of larger cells (the mother-cells of the spores) 

 with grumous contents and large nuclei, surrounded imme- 

 diately by a layer of delicate, mucilaginous, radially- 

 extended cells, similar to those which surround the string 

 of mother-cells of the anthers of phsenogams. This layer 

 is followed by a layer of tabular, thick-walled, chlorophyll- 

 bearing cells, which supports the epidermis of the sporan- 

 gium : these chlorophyll-bearing cells are radially-extended 

 prismatic cells with watery fluid contents ; in the young 

 fruit they are four times smaller than the chlorophyll- 

 bearing cells immediately below : when the fruit is 

 almost ripe they are — in consequence of repeated divisions 

 - — almost sixteen times smaller than the same cells (PL 

 LV, figs. 5, 6, 16). 



This multiplication of the cells of the young sporangium 

 takes place mainly in the direction of the breadth ; the 

 organ assumes the form of a laterally-flattened ellipsoid, 

 which in the macrosporangia passes by degrees into the 

 shape of a kidney, and in the microsporangia becomes 

 more elongated. The leaf in whose axil the sporangium 

 originates, does not begin to develop its stipule until a 

 later period, when the young fruit has attained a con- 

 siderable size, and the central group of spore-mother- 

 cells has almost completed its full number (PI. LIV, 

 figs. 3, 4). 



The mode of development of the sporangium shows 

 most distinctly that the latter cannot be considered as a 

 transformed portion of a leaf, unless * the group of cells 

 which is formed close above the place of insertion of the 

 stipule, above the apex of the angle between the latter and 

 the stem, is considered as belonging to the leaf and not to 

 the stem. This supposition is only difficult to reconcile 

 with the observed youngest conditions of the leaf and spo- 

 rangium. The young rudiment of the fruit, when consist- 

 ing of only very few cells, is generally situated on the 

 outer surface of the end of the stem (which outer surface is 

 turned towards the leaf,) even in those species, like Sela- 

 ginella helvetica and spimdosa, whose sporangia, when only 



* See von Mold ' Vermischte Schriften/ p. 106. 



