4J4 



VASCULAR CRYPTOGAMS. 



traces back also the origin of the spores in Selaginella to a single primary mother- 

 cell, which is the central cell of the sporangium. All that is known in addition about 

 Lycopodium and Psilotum is that the first point is at least not universal, while 

 Russow, 1 think rightly, has doubts about the latter. 



In Isoetes the sporangia originate, according to Hofmeister, from the leaves in 

 their very earliest stage. A single cell produces the mass of tissue, of which two 

 outer layers of cells (Fig. 306 B) become the wall of the sporangium, while strings 

 of cells running transversely form the trabeculae. The numerous cells which lie 

 between the latter still remain united into a tissue, increase in number, and form the 



Fig. 309. — Development of tlie sporangia and spores oi Selaginella ijiaqjtalifolia ; the order of succession is indicated 

 by the letters A—D ; A and B serve for all the sporangia. C and D for the microsporangia only ; H division of the mother- 

 cells of the microspores, h four nearly ripe spores ; in ^, C and D, a, b, c are the three layers of the wall of the sporangium, 

 d the primary mother-cells (A, B and E X 500 ; C and D X 200). 



mother-cells of the spores ; they finally become isolated and rounded oif. The 

 spores are formed by a repeated bipartition of these spore-mother-cells in planes at 

 right angles to one another. 



In Selaginella again, according to Hofmeister, the sporangium springs from a 

 mother-cell which belongs to the periphery of the stem. In later states the spor- 

 angium is inserted in the axil or even in the base of the leaf. As in Isoetes, the 

 fibro-vascular bundle of the leaf runs beneath the sporangium, without sending a 

 branch into it {cf. Psilotum, infra). I was unable, even in the youngest which came 

 under my observation, to recognise a central cell which could be considered the 

 mother-cell of the spores ; on the contrary, even in very young sporangia a separation 



