374 TRANS. ST. LOUIS ACAD. SCIENCE. 



5. According to the presence or absence of peripheral bast- 

 bundles : 



a. Without bast-bundles : I. lacusiris, I. pygnma^ I. Tuckermafti, 

 I. echinospora^ I. saccharaia, I. Bolanderi^ I. t'iparia^ and /. fnela- 

 nospora. 



b. With bast-bundles: /, Engelmanni^ I. Howelli^ I. Jlaccida^ I. 

 melanopoda^ I. Bittleri, I. Nuitallii^ and /. Cubatia. 



The comparative size or the sculpture of the spores, and the 

 number and length of the leaves, furnish no legitimate grounds 

 for classification ; still it may be mentioned here, that the largest 

 macrospores (0.45 to 0.80 mill, in diam.) are found in /. lacustris, 

 I. Bufleri, and /. riparia ', the smallest (0.25 to 0.45 mill.) in /. 

 mela7iopoda, I.Jiaccida, and /. Engel/7ianni var. valida. 



The largest number of leaves, 50 to 200, are observed in the 

 last mentioned form, in /. melatwpoda and in /. Nuttallii; the small- 

 est number, 5 to 20, in /. pygmcea^ I. melanospora, I. saccharata, 

 and /, Bolanderi. 



The longest leaves (15 to 25 inches long) we meet with in /. 

 Engelmanni, I. Jlaccida, and /. Cubana; the shortest (2 to 3 inches 

 long) in /. pygmcea, I. melanospora, and /. saccharata. 



The following classification of our species is proposed as the 

 best I can find, though by no means a faultless one. 



I. Trunk bilobed. 



A. Submerged species with quadrangular leaves, without, or in 4 and J with 



few or many stomata and without peripheral bast-bundles; velum in- 

 complete. 



I. /. lacustris. 2. /. pygmcea. 3. /. Tuchermani. 4. /. 

 echinospora. 5. /. Bolanderi. 



B. Amphibious species with abundant stomata in the quadrangular leaves. 



' * Without peripheral bast-bundles (these are intermediate be- 



tween the submerged and the truly amphibious species.) 



f Velum partial. 



6. /. saccharata. 7. /. riparia. 



t t Velum complete. 



8. /. melanospora. 



* * With peripheral bast-bundles. 



f Velum partial. 



9. /. Ettgelmatini. 10. /. Ho-velli. 



t t Velum complete. 



11. /. jiaccida. 



C. Terrestrial species, maturing when entirely out of water, with abundant 



stomata and peripheral bast-bundles in the nearly triangular leaves. 



* Velum partial or almost wanting. 



12. /. melanopoda. 13. /. Butleri. 



