ENGELMANN THE GENUS ISOETES IN N. AMERICA. 371 



fully exposed to the hot sunshine of that season. Three weeks 

 later the first green points were seen and continued to come up 

 until the end of October, while at that time the earlier ones had 

 already developed 5 to 8 leaves, J to 1 ^ inches in length. The 

 contents of the large or female spore-cell first developed into a 

 dense cellular mass ; this, enlarging, split the cell-coats as above 

 described and protruded obliquely upwards a minute conical 

 point, green inside, while on the lower edge of the opening, but 

 still between the three valves (the lower hemisphere of the spore- 

 case not being ruptured or perforated at all), a much smaller and 

 rounded knob, the origin of the first rootlet, showed itself, bear- 

 ing a large number of extremely fine capillary fibres ; the bulk of 

 the prothallus remained enclosed in the hemispherical part of the 

 spore-case as a lateral knob, while the first leaf and then the first 

 rootlet elongated ; the spore-case was thrown oft' only when the 

 former had acquired a length of 3 to 4 and the latter one of 2 to 



3 lines, the capillary fibres still continuing at the origin of the 

 rootlet. Soon afterwards a second leaf and a second rootlet were 

 formed, both opposite to the laterally protruding spore-mass ; after 

 that new leaves and new roots spring up in distichous order 

 between the older ones, the youngest in the centre. In twelve 

 months the young plant, not yet fertile, shows the bilobed flat 

 or rather concave trunk, 2 to 4 lines in diameter, with both ends 

 strongly elevated, their edges already showing small masses of 

 black decayed tissue (the remnants of the first year's gi-owth). 

 The leaves of these yearling plants, 10 to 15 in number, are 3 to 



4 inches long, have abundant stomata, but as yet only a single 

 very slender bast-bundle, median on the upper surface. 



The species oi Isoetes^ perhaps 40 to 60 in number (according 

 to the views taken of the different forms, whether species or 

 varieties), are distributed over the whole globe, apparently more 

 abundant in the temperate than in the tropical zones. In North 

 America we have 13 species, with i 2 varieties, to which I add one 

 from Cuba ; from Mexico we have received as yet none. More 

 are expected to be found when the attention of collectors is more 

 earnestly directed to them. 



Most of the species may be called water-plants, growing in 

 stagnant or in slow-running water ; a few are always submerged 

 and are found out of water only in abnormal conditions, e.g. in 



