CHAPTER XI 



SOME MISCELLANEOUS EXAMPLES OF HETEROGENESIS 



(a) On the Relations between certain Diatoms and the 

 Fission Products of a parasitic Alga (Chlorochytrium). 



MUCH interest was excited in 1872 owing to the discovery by 

 F. Cohn ' of an Alga existing, as a parasite, in the thallus of 

 the ivy-leaf Duckweed (Lemna trisulca). This was followed in 

 1877 by the discovery of another parasitic Alga by Prof. Perceval 

 Wright '^ infesting various marine Algse. Since this time, several 

 other forms have been discovered, and rather an extensive 

 literature has grown up concerning Chlorochytrium and allied 

 genera. 



Among the new forms there is one Ch. Knyanum, found in 

 Lemna gibba and in L. niinor^ which was examined and figured 

 by G. Klebs3 in 1881. This is evidently the Alga that I have 

 of late met with very abundantly in both these species of Duck- 

 weed, and to which my present remarks will refer. 



I found, during the autumn and winter of 1902, among Duck- 

 weed from various localities, many dead and decolourised leaves, 

 having a greyish-white and somewhat gelatinous appearance. 

 Such leaves may be easily picked out, by spreading some of 

 the Duckweed in a thin stratum of water over a white dish. It 

 will then be found that the decolourised leaves are all devoid of 

 rootlets, and possibly this loss of the rootlets may have been the 

 main cause leading to the premature death and to the change 

 in the appearance of the leaves. 



Examination with a hand lens, magnifying eight or ten diameters, 

 will show, in many of such leaves, that the upper greyish-white 

 surface is flecked with minute specks of an emerald-green colour,4 



" " Beitriige zur Biologie der Pflanzen," Heft ii., p. 87, 

 = " Trans. Roy. Irish Acad.," vol. xxv., p. 13. 

 3 " Botan. Zeitung," 1881, 248, t. iii., p. 11-15. 



* The changes, now to be described, were found to be very much less common 

 in 1903 and 1904. 



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