OF HETEROGENESIS 211 



weeks later I examined the leaflet again, and found, in the same 

 patch, that some of the corpuscles were still single and colourless, 

 while others of them were pale blue-green, or pale blackish- 

 purple in colour : intermediate conditions were also recog- 

 nisable. Those that were coloured in the way I have indicated 

 were either single, or had grown into chaplets of three, four, or 

 more elements such as are shown in B ( x 500). The same kind 

 of changes were going on in the other patch of decolourised 

 chlorophyll corpuscles. Yet all of them were contained within closed 

 spherical cells covered by an uninjured epidermis on each side of the leaf. 



For two weeks more I examined this leaflet from time to time, 

 and found the same changes slowly progressing. Soon afterwards 

 they seemed to cease. The continued examinations, as well as 

 the confinement indoors in a small tube beneath a bell-jar, were 

 doubtless not a little unfavourable. Still the trichomes of Anabena 

 grew in length, and increased in number, varying somewhat in tint, 

 but being mostly of a pale purplish-black colour. 



Here again the heterogenetic transformation was actually seen 

 occurring within the closed cells of the Duckweed ; into which the 

 non-motile spores of Anabena had no means of getting. 



(d) Transformation of the Contents of the Resting Spores 

 of a small Spirogyra into a number of Amoebae. 



A specimen of a small Spirogyra (known as S. quadrata)^ having 

 the lateral mode of copulation, was found in the month of April 

 in a small pool from which most of the water had evaporated. 

 A portion of this weed was placed in a shallow pot on the mantel- 

 piece, only just covered by water, and under a small glass shade. 

 After about one week the weed began to die, and towards the end 

 of the next week many of the resting spores (which survive and 

 remain green much longer than the filaments in which they have 

 been formed) were seen to be undergoing the changes now to be 

 described. 



The resting spores of this species of Spirogyra have an ellip- 

 soidal shape, and on examination with the microscope their green 

 contents can be seen to be largely composed of the nuclear-like 

 bodies of the bands of the two cells by whose fusion the spore has 

 been formed. These bodies may be recognised in Fig. 33, A 

 (x 250). In other specimens some of these bodies seem to have 

 fused so as to give rise to a smaller number of rather larger 



