FRESH-WATER ALG^ OP THE UNITED STATES. 105 



formed. Near to the larger or central end of each of these now appears a pouting 

 transparent nipple-like process. The corresponding opposing processes enlarging 

 and meeting coalesce, so that the upper half of one closterium, in the form of a 

 daughter-cell, is finally united with the upper half of the other closterium, and the 

 two lower halves are also joined together. Thus from a single pair of fronds arise 

 two conjugating pairs of cells, and finally two sporangia, in each of which a spore 

 is perfected. 



This process does not seem, however, to be universal amidst the Closteria, for 

 in many, if not all, of the smaller species, a pair of fronds produces a single spo- 

 rangium. 



In the genus Palmogloea, in which 1 have had an opportunity to study the devel- 

 opment of the spores, the process closely simulates that seen in certain of the 

 Spirogyra. The contents of the cells first became broken up and confused, and 

 almost simultaneously the nucleus disappeared (fig. 4, pi. 11) the cells became 

 swollen at one side and slightly bent backward so as to form jutting processes, 

 which meeting grew together, became confluent and developed into a sporangium 

 much larger than either of the parent cells. Into this sporangium the contents of 

 the latter passed and soon became converted into a thick-walled spore (fig. 00, pi. 

 00) often completely filling the cavity, and apparently with its waU adherent to that 

 of the latter. 



Genus PALMOGLCEA, Ktz. (1843). 



Cellulse oblongae, ellipticae vel cylindriese, utroque polo rotundatse, medio non constrictae, pleromque 

 in muco gelatinoso nidulantes, liberse, singulae vel in familias consociatse, lamina chlorophyllacea 

 axili vel excentrica, aetate provecta medio constricta, denique divisa prasditse. (R.) 



Syn. — Mesotsenium, N^geli. 



Cell oblong, elliptical or cylindrical, rounded at each end, not constricted in the middle, mostly 

 swimming in a gelatinous mucus, free, single or associated in families, chlorophyl lamina axillary 

 or excentric, in the early state constricted, and at length divided in the middle 



Remarhs.—The above diagnosis of the genus is that given by Prof. Rabenhorst, 

 and agrees essentially with that of De Bary, Nsegeli, &c. In the species herein 

 described however, the axillary lamina of chlorophyl were not so pronounced, for 

 the green coloring matter seemed often to surround the cavity of the cell, and in 

 other specimens was broken up and diffused through it. 



P. clepsydra, Wood. 



P. saxicola et bryophila, in gelatina achroa interdum dilute viride nidulans ; cellulis cylindricis, 

 cum polis obtuse truncato-rotundatis, diaraetro 2-3 plo longioribus ; lamina chlorophyllacea 

 axili, plerumque indistincte, saepe nulla; plasmate dilute viride; nucleo plerumque distincto; 

 zygo'sporis subfuscis aut subglobosis aut enormiter in clepsydrae forma; membrana externa 

 enormiter excavata et sulcata. 



IHam.—i,\%js". 



Syn.— P. clepsydra, Wood, Prodromus, Proc. Amer. Philosophical Soc. 1869. 

 JTaft.— In rnpibus et in muscis irroratis ad Chelten Hills, prope Philadelphia. 

 14 June, 1872. 



