246 University of California Publications in Botany [Vol.8 



a fashion as to be insufficient in itself for diagnosis. The anatomical 

 characters, on the other hand, seem to be more reliable, but, of them- 

 selves, present difficulties and seeming abnoraialities or departure from 

 type. Very few of the older species have been carefully described 

 anew from the type specimens, so that uncertainty holds in many 

 cases as to the exact application of specific names. Different writers, 

 also, differ decidedly as to their views of specific limits and groupings 

 of forms, so that a student of this group fiiids much variance of 

 opinion, and consequent resulting confusion. 



We have followed the accounts of Collins (1903 and 1909, p. 195 

 et seq.) very largely, but with due attention to the revision of J. G. 

 Agardh (1883, p. 115 et seq.) and the critical remarks of Reinbold 

 (1889, p. 113 et seq.), Borgesen (1902, p. 487 et seq.), Jonsson (1903, 

 p. 343 ct seq.) and Kylin (1907, p. 4 et seq.). Very considerable 

 assistance has been obtained also from the earlier monograph of the 

 group by Ahlner (1877) especially as interpreted by J. G. Agardh. 

 Study has been made of the living plant so far as possible, and dried 

 specimens have been boiled in water before examination to restore cell 

 outlines and chromatophores. This method of preparation has given 

 very satisfactory^ results, the dried specimens swelling up and assum- 

 ing a form and structure closely approximating that of the living 

 material. Even the chromatophores are fairly well restored to size, 

 shape and position. 



The species of Enteromorpha inhabit brackish water and strictly 

 fresh water as well as strictly salt water and that which passes for 

 the same species may be found in all three. The amount of salinity 

 of the water may, seemingly at least, have very different effects par- 

 ticularly upon the branching and the thickness of the membrane. 

 Careful cultures, however, are needed to establish this fact clearly and 

 convincingly. It may be stated that the culture of various species 

 and forms of the different species of Enteromorpha is very necessary 

 before a definite basis for many of the distinctions now employed may 

 be assured. 



The species of Enteromorpha are probably more nearly "cosmo- 

 politan" than thase of any other genus of marine algae, although 

 the term cosmopolitan can not, in all probability, be used in the 

 strictest sense, even in connection with them. The ranges of the 

 different species along our western coast of North America are more 

 extensive than those of the species of most other genera. This is to 

 be explained, we think, by the fact that the species of Enteromorpha 



