12 



INTRODUCTION. 



In examining the rising sporangia of Physarum nutans in 

 a moist chamber under the microscope, the projecting masses of 

 plasm odium are seen to pulsate, distending and shrinking as the 

 rhythmic flow advances or retreats, but gradually gaining with the 

 advancing movement. The basal part of each contracts and forms 

 a stalk consisting of a tube of tougher hyaline substance through 

 which the protoplasm continues to pass until the surrounding veins 

 have emptied their contents into the spherical sporangium. The 

 coarse refuse matter which has not been discharged along the track 

 of the plasmodium, where it often takes the form of a hypothallus 

 connecting the sporangia, is deposited in the centre of the stalk. 

 When the young sporangium has attained its full dimensions, 



the wall thickens, and a 

 part of the lime granules 

 which abounded in the 

 plasmodium is incorpo- 

 rated in the wall-sub- 

 stance ; the remaining 

 part is collected into the 

 lime - knots or vesicular 

 swellings of the hyaline 

 threads of the capilli- 

 tium ; these threads 

 branch and anastomose, 

 forming a network which 

 spreads through the 

 spore - plasm from the 

 base of the sporangium 

 to its wall. The forma- 

 tion of spores takes place 

 after the capillitium has 

 been developed in all 

 the genera which are 



FlG. 7. COMATRICHA OBTUSATA PreUSS. 



From a stained preparation of a young sporangium, 

 showing the pi asm odium separated into rounded masses 

 about groups of nuclei, which are dividing by karyo- 



kinesis ; the nuclear division has reached the "spindle , , , 



stage" ; the spindles are seen in profile in all cases but Characterised by its 

 one in which the equatorial plate is seen from one of 

 the poles of the spindle. 



Magnified 1200 times. 



CPYIPP 



e ' 



Tn 



the 



lime-granules 



which 



can be seen in the 

 plasmodium are dissolved in the sporangium, and the salt in 

 solution passes through the soft sporangium -wall and forms 

 into crystals on the outer surface. The various kinds of 

 capillitium represented in the different genera and species are 

 described in the text. The formation of spores in the Endo- 

 sporece is preceded by the division of the nuclei in the spore- 

 plasm by karyokinesis. The process was first recorded by 

 Strasburger as occurring in Trichia fallax.* Recent observa- 

 tions show that this mode of nuclear division takes place in the 

 sporangium only once, and occurs almost simultaneously in all 

 the nuclei rather more than an hour before the spores begin to be 



* Botanische Zeitung, May 1884. 



