126 



On the Genus Isoetes. 



ton calls them " bluntly tubercled,") whilst in Durim they are 

 deeply pitted or honeycombed. 



Mr. Baker, curator of the Kew Herbarium, after an ex- 

 amination of the Guernsey plant, pronounced it to be the 

 Isoetes hystrix, var. subinermis of Durieu, adding to his note 

 " we have the same form in Kew Herbarium from Caprera, 

 Algeria, French Landes, Phrygia, Smyrna, Castille, etc., it is in 

 fact more common than the typical hystrix with the big 

 spines.' ' 



The species of Isoetes of which I have chiefly been speak- 

 ing (including all the British species) may perhaps be tabulated 

 thus 



Aquatic, without persistent leaf bases, growing at 

 bottom of lakes and pools in Britain : 



Csespitose, leaves erect, green , . lacustris. 



Solitary, leaves spreading, pale echinospora. 



Terrestrial, with persistent leaf bases, resembling 

 scalesy growing in exposed sandy places : 

 Scales with two long subulate horns, 

 and an intermediate tooth, macro- 

 spores bluntly tubercled (West of 



France) hystrix. 



Scales with three teeth, macrospores as 



above (Guernsey) . . hystrix var. subinermis. 

 Scales with teeth, macrospores pitted, 

 much larger and more robust than 



the last (Algiers) Durim. 



A very interesting question suggests itself with respect to 

 the propagation of Isoetes hystrix. How are the spores dis- 

 seminated ? The sporangium or sporesac is incorporated with 

 the base of the leaf, and the rhizome or bulb from which the 

 leaves spring is buried an inch or two in the earth. Now, if 

 the plant grew on loose drifting sand dunes, we could readily 

 imagine the mature sporangia becoming detached and after- 

 wards blown about by the wind, but instead of this it grows in 



