XX INTRODUCTION. 



lanospermeae) contains sea-weeds of the larg-est size^ 

 if not of the most complex structure 5 some have 

 the frond developed into a distinct stem with leaves 

 and receptacles containing the spores. The red 

 series are remarkable for the delicacy of their tissue, 

 and for possessing a double system of fructification, 

 that is, producing- both spores and tetrasporeSy while 

 the grass-green series (Chlorospermese) possess the 

 simplest structure, and their seeds, at certain 

 periods, are endowed with a singular power of loco- 

 motion, whether voluntary or not is still a matter 

 of dispute amongst botanists. Though the colour 

 may often serve as an index whereby to determine 

 the series, &c., to which a species belongs, the young 

 student must be careful not to trust too implicitly 

 to this guide, taking care to collect such plants as 

 grow in a favourable situation for the development 

 of their natural hues. Many of the red series, 

 when growing in unfavourable situations, assume a 

 yellowish-green, or whitish colour. ^^Laurencia 

 pinnatifida," Dr. Harvey observes, '^ is particularly 

 variable in this respect. When this species grows 



