THE ISOETACE^E. 215 



usually sufficient to indicate the group to which the 

 plant belongs, but other considerations must often be 

 taken into account in naming the species. In the fol- 

 lowing pages, illustrations of the megaspores only have 

 been given. These all have the same magnification, so 

 that the comparative size of the spores may be easily 

 seen. It is expected that when the plants are better 

 known than at present the species will be more easily 

 distinguished, because more accurately described. Fur- 

 ther notes on all our species are greatly desired. 



The word Isoctcs is said to be derived from two Greek 

 words meaning " equal " and "year," and was applied to 

 these species because of the perennial character of the 

 leaves. The species are widely distributed throughout 

 the world, but are most plentiful in the glacial lakes and 

 the streams leading from them in the northern hemi- 

 sphere. They are an isolated group not closely con- 

 nected with any other living forms, but exhibiting in 

 their structure certain features that seem to indicate 

 that the modern monocotyledons, to which the grasses, 

 lilies, and orchids belong, may have arisen from the 

 same parent stem. As recognised at present, Isoetes is 

 the only genus in the family Isoetacese, and this family 

 the only one in the order Isoetales. 



