86 



found a cell-wall round the alga (p. 26)^ and even without that 

 it is very unlikely already — . Still I have obtained a number 

 of observations with cultures of isolated green algae, from which 

 seems to follow that sometimes the number of oildroplets, which 

 occur outside the algae c. q. free in the membrane at the bottom 

 of the culture, rises and lowers with the number of oildroplets 

 within the algae, that is to say with the number of algae lodging 

 such a droplet. See Table 11. 



In general, namely, the free oildroplets seem to disappear very 

 soon from an algal-culture. Quite intelligible, for instance by the 

 action of bacteria. Further it appears, that these free droplets 

 can only be numerous if there are also numbers of algae con- 

 taining an oildrop ; if the number of the latter lowers ' — which 

 always happens when the algae are vigorously dividing — that 

 of the former seems to necessarily follow immediately. Is the 

 reverse the case (with rising, namely), this need not absolutely 

 take place. Sometimes however this happens in quite a striking 

 way. I will give an example: A culture in light of numerous 

 green algae, several of which carry an oildroplet, very rarely 

 shows a free oildroplet. After 10 days the number of green algae 

 with oildroplets has increased very considerably, the number 

 of free oildroplets also to rather a great number. Two cultures 

 are made then out of this one, and one of them is placed in 

 light under favourable, the other under unfavourable conditions. 

 After two weeks again the first culture shows a particularly high 

 number of green stages of division of the algae, consequently a 

 small number of algae with oildroplet, and also a small number 

 of free oildroplets; the 2"^ culture on the contrary contains no 

 stages of division , numerous algae with oildroplet and rather 

 a great number of free oildroplets. Now follow the first of these 

 two cultures. After a month this one shows very seldom a stage 

 of division and consequently a great number of algae with oil- 

 droplet ; yet free oildroplets are only present sporadical ; but three 

 months later, when dividing-stages lack and thus oildroplets still 

 appear in a great number of algae, the free oildroplets have be- 

 come rather numerous again. 



