146 FRESHWATER ALG.B. 



not familiar by reference to our sketch. [Plate HE., Fig. 7.]* Two 

 individuals approach one another, and a communication being 

 established between them through the bases of their separated halves, 

 the cell-contents are poured out into the intervening space and there 

 form a spore, generally spherical and at first smooth, but in the mature state 

 often ox'namented with tubercles or spines. In this condition the structure 

 and markings of the empty cellulose cases are beautifully displayed. 



Wliat is the exact series of changes by which the original form is 

 developed from the spore requires further investigation, in spite of 

 Berkeley's statement that it is pi'opagated in some species by division, 

 exactly after the fashion of the ordinary cells, and in the third generation 

 acquires its normal form. 



Other points in the physiology of these plants also await further 

 research, as, for instance, the nature of the cui'ious circular hyaline 

 spaces filled with moving granules, which are seen in the ends of the 

 frustules of Cloaterium and Peniiim; the circulation of similar particles 

 between the cell-walls and the endochi-ome ; and the remarkable 

 "swarming" of the entire cell-contents, which occurs in some genera, 

 probably before conjugation, when every gi-ain of endochrome seems to be 

 rushing wildly in and out among its fellows in a sort of giddy dance. 



Passing from the unicellular to the filamentous Algro, which consist 

 for the most part of elongated cyhndrical cells placed in juxtaposition, 

 end to end, in vaiaous arrangements, we are compelled by want of space 

 only to glance at many large and interesting orders. Among these are 

 the Batrachospermecc, represented by the exquisitely graceful genus 

 Batrachosj^ermum, whose gelatinous tresses of tender gi-ey or ohve gi-een 

 whorled branchlets are not uncommon in clear streams in tliis district; 

 the almost equally beautiful Cha-tophomcea;, of which abundant examples 

 are to be found in the deep green gelatinous masses of Clmtophora 

 cndlvuefolia &ndC.ele[)anx, inthe tender gi-een filaments of Draparnaldia 

 plumosa waving gracefully in clear running waters, and in the singular 

 disk-shaped fronds of Coleochmte scutata, found adlierent to leaves of sub- 

 merged aquatic plants ; the OttciUatoriacea; which comprise many 

 singular forms, inhabitants of pools, wet rocks, damp gi'ound, &c., and 

 well represented in our district ; and finally the Nostochacecr, of which the 

 tjTpical genus Nostoc contains many species, consisting of long beaded 

 filaments, twisted like intricate coils of rope, and agglomerated into 

 gelatinous fronds ranging in size from that of a pea to that of a walnut, 

 most cosmopolitan in their habitats, rejoicing in situations so various as 

 clear streams, exposed moorlands, and thatched roofs. 



In what remains of this paper we pui-poso to refer in some detail 

 to throe of the remaining groups of Confervoid Algro, each of which 

 presents interesting points of structure and remarkable aspects of the 

 phenomena of rci)roduction. 



First among these is the large family of Sijihonacdr, of which the 

 commonest examples are the various species of Vaucheria, some of which 



♦ The fignrcs given in these papers are all drawn nnderthe microscope, from 

 actual specimens. We do not hesitate to insert them, because those given in text 

 books are often only diagrammatical, and convey but an imperfect idea of the actual 

 object. 



