48 THE MYCETOZOA 



The presence of substances suitable for food exercises a strong 

 attraction on plasmodia. When the spreading border touches 

 such a substance the streaming movement is at once quickened in 

 this direction, and the outlying lobes being drawn in, the whole 

 plasmodium is rapidly concentrated on the nutrient material (14). 



The contrary effect is seen when harmful substances are brought 

 into their neighbourhood. 



The plasmodia of many species are said to shun the light, but 

 this is not the case with all ; that of Badhamia utricularis, for 

 example, will, if a moist atmosphere be maintained, continue to 

 spread over the pilei of the fungi on which it feeds, though these 

 may be exposed to full sunlight. 



Nuclei. The plasmodia are multinucleate from their origin; 

 but from the fact that a minute plasmodium a few millimetres in 

 diameter will grow, when supplied with food, till it is many inches 

 in diameter, and that the nuclei are then as numerous, in a small 

 sample, as they were before the growth had occurred, it is clear 

 that the nuclei increase in number pari passu with the growth of 

 the protoplasm. There is reason to believe that this increase occurs 

 in two ways, (a) A simultaneous division of the nuclei by karyo- 

 kinesis has been found to be in progress when plasmodia (of Badhamia 

 utricularis, Fig. 7, c-f) are stained (17, p. 541) a process comparable 

 apparently with the simultaneous division of nuclei which occurs in 

 the vegetative stage of Adinosphaerium. (b) Multiplication by simple 

 division is not easy to establish, where, as in this case, prolonged 

 observation of the nuclei in the living state is rendered difficult by 

 the movement of the plasmodia, but the following observation appears 

 to show that it is of frequent occurrence in their growth :. 



A plasmodium of Badhamia utricularis, spreading and feeding on 

 the pilei of the fungus Auricularia, increased in size about fourfold 

 in fourteen hours ; and during this time a small portion of it was 

 removed, smeared on a cover-slip, and fixed every quarter of an hour. 

 On staining the 56 samples so obtained, the nuclei were found to be 

 approximately equally abundant in all, and presented considerable 

 differences in size, but in no case was there any indication of karyo- 

 kinetic division. Now in the karyokinetic division of nuclei which 

 occurs prior to spore-formation (see p. 52) the process lasts from one 

 to one and a half hours. Assuming the same duration for the 

 karyokinetic division of the nuclei in the growing plasmodium, and 

 bearing in mind that the division in this manner, when observed, 

 was simultaneous, we must conclude that it had not occurred in 

 the fourteen hours during which the observations were made ; yet 

 from these observations it appears that in this period the number 

 of the nuclei had increased about fourfold (18, p. 9). As a fact, 

 the appearance of the nuclei in various phases of constriction is of 

 common occurrence when stained plasmodia are examined with a 



