OF HETEROGENESIS 209 



obtained enti^ to the spaces in question. He did not attempt to 

 verify this assumption ; he seems to have taken it for granted, 

 in accordance with generally received doctrines, that this was the 

 proper explanation to be given. 



I have never met with either of the first three organisms, 

 named above, in the Chlorochytrium spaces, but I have, on many 

 occasions, seen one of the Nostoceae ; and am prepared to adduce 

 evidence as to its mode of origin within these cavities. I have, 

 however, never seen the slightest evidence in proof of the 

 assumption that they get in from without. Cohn says he found 

 a representative of the genus Nostoc, but the organism which 

 I have seen is, apparently, an Anabena. The filaments were free, 

 and certainly not imbedded in any mucilage or jelly-like matter. 

 And in reply to a query of mine Dr. M. C. Cooke writes, " filaments 

 without the definite mucilage do not, to my mind, constitute a true 

 and veritable Nostoc. I could only suggest Anabena, with free 

 filaments, as an alternative to Nostoc." 



It must be borne in mind, however, that the filaments in each 

 of these genera are endowed only with a minimum amount of 

 mobility, of an oscillating type, and that their spores are non- 

 motile; so that the conditions are very unfavourable to their 

 parasitism within closed cavities, or cavities with apertures only of 

 the most minute dimensions. 



I have found that specimens of Lemna containing these Algse, 

 when mounted in a mixture of glycerine and formalin ' are well 

 preserved, and are in some respects more favourable for examina- 

 tion than when they are simply immersed in water. The colours 

 of the Nostoceae are preserved extremely well in specimens thus 

 mounted. 



Just the same kind of combinations are to be met with as in the 

 case of the transformation of the fission products of this Alga into 

 Diatoms — that is, the Anabena and the Chlorochytrium may be 

 found mixed in the most varied proportions, or the Chlorochytrium 

 may be completely replaced by the Anabena. Moreover, in 

 specimens of the former kind, the individual elements of the 

 Chlorochytrium may often be observed actually undergoing the 

 process of transformation into Anabena, and changing in colour 

 from green to blue, purple, or even red. This process of transfor- 

 mation may be seen taking place in a sub-epidermal space which 



' One part of glycerine to two parts of a 2 per cent, solution of formalin 



14 



