A Igae and the Principles of their Evolution, i o r 
material obtained partly in nature and partly by the aid of 
pure cultures, some of them under the microscope. I have 
drawn no conclusions from my work which are not based — 
firstly, on the fact that on the same plant (filament or colony) 
forms which had been formerly considered as distinct grow in 
direct connexion ( Cystococcus , Pleurococcus') ; secondly, on the 
observation under the microscope of the production of spores 
and zoospores in plants which up to now were considered 
destitute of them (zoospores oi Eremosphaer a, scores oi Scene- 
desmus , larval condition of Chlamydomonas ,&c.) ; thirdly, on the 
fact that in a pure culture all the individuals, or nearly all, 
underwent a transformation which could be easily followed 
(filament of Pleurococcus , the fixed forms of Raphidium , &c.); 
and, fourthly, on the observation that under changed conditions 
the new forms are always in relation to their surroundings 
( Palmella , Monostroma , Pediastrmn). All these observations 
have been verified a great many times h 
Which are the lowest of the Green Algae it is not easy 
to say, because the most simple, namely, those from which 
I am inclined to derive the others, are still very highly 
organized, and those apparently less complex are merely 
reduced forms. Hence it would not be possible for a philo- 
sopher to take the lower Green Algae as a basis for the 
theory of the origin of life. 
It is permissible, however, according to my observations, 
to trace the principal groups of the Chlorophyceae back to 
the little order of the Palmellaceae, in which are comprised 
the following genera : Palmella ( miniata ) 2 , Tetraspora , Gloeo- 
cystis and Apiocystis. 
Palmellaceae. Their gelatinous general envelope is pro- 
duced by the confluence of the special gelatinous cell-walls. 
In Palmella the cells are grouped together in all directions 
of space ; whilst in Tetraspora they are regularly disposed 
1 These observations are quite independent of the theories of polymorphism 
which were formerly advanced by Kiitzing, Hansgirg, and Borzi, and which were 
not derived from direct observations or pure cultures. 
2 See Chodat, Materiaux pour servir a l’histoire des Protococcoidees, Bull, de 
l’Herbier Boissier, 1894, t. 2, p. 585. 
