BesmicUecB.'] micrasteeias. 363 



interest, both as it relates to themselves,, and in the remark- 

 able manner in which it takes place, and because it unfolds 

 the nature of a process in other families ; and furnishes a 

 valuable addition to the knowledge of their structure and 

 physiology. The process is very evident in the genus 

 Euastnim, for, though the frond is really a single cell, yet in 

 all its stages it appears like two, the segments being always 

 distinct, even from the commencement, being separated 

 from each other by the length of the connecting tube, 

 which is converted into two hyaline lobes. These lobes, 

 increasing in size, acquire the colour, and gradually put on 

 the appearance, of the old portion. Of course, as they in- 

 crease, the original segments are pushed further asunder, 

 and at last are disconnected, each new lobe taking with it 

 an old segment to supply the place of that from which it 

 was separated, so that every new specimen of Euastrum 

 is partly new and partly old. A single glance, however, at 

 Mr. Ealfs^s Plate xi. fig. 2, Euastnmi vernccosumy will give 

 a better idea of this than all the words we can employ. 



MICRASTEEIAS, AgardL 

 Gen. Char. Fronds simple; lenticidar, deeply divided into two 



