INTRODUCTION 



17 



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 formed. It is 

 difficult to ascertain the exact number of the chromosomes 

 on account of their small size ; Harper* counted twelve in 

 Fuligo, and Jahnf considers the number in Trichia and Arcyria 

 to be sixteen (" eight double chromosomes "). 



In Badhamia, Physarum, Craterium, Didymium, Stemonitis, 

 Lamproderma, and Comatricha, when the spindle stage is 

 reached, the plasma breaks up into lobed masses containing 

 six to ten nuclei (fig. 7). During the later stages of nuclear 

 division these become sub-divided until reduced to masses of 

 two spores' capacity, 

 each containing a pair 

 of nuclei resulting from 

 .a, division (fig. 8). By 

 a final constriction these 

 divide into the ultimate 

 spores, each containing 

 a single nucleus. In a 

 short time the spore- 

 wall is acquired, and 

 the active stage of the 

 organism comes to a 

 ■close. 



In the genera just 

 mentioned, spore-forma- 

 tion occurs in warm 

 weather about twenty 

 hours after the sporangia 

 have taken form. In 



Trichia the interval is much longer, extending from 

 two to four days according to the temperature. In 

 this genus and also in Arcyria, Lycogala, and Reticularia 

 the spore-plasm is not seen to separate in lobed masses at 

 the time when the nuclear spindle is formed, but the 

 karyokinetic process is completed and the daughter-nuclei 

 a,re definitely parted from one another before the plasma 

 breaks up and encloses each nucleus in a young spore. 



The sporophores of Ceratiomyxa are columnar, or confluent 

 and interlacing. In their early stage the protoplasmic matter 

 ispreads throughout the superficial part of the columns, and 

 also in numerous veins traversing the watery gelatinous 

 interior substance. These veins are ultimately withdrawn 

 to the outer layer, where they form a close network. The 



Fig. 8. — Comatricha nigra Schroeter. 



From a stained preparation of a young spor- 

 angium, showing the plasma separated into 

 masses of two spores' capacity round the nuclei, 

 which have almost divided by karyokinesis. 



Magnified 1200 times. 



* Botanical Gazette, xxx. 217 (1900). t Myxomycetenstudien — 6. Kernversch- 

 melzungen und Reduktionsteilungen," Ber. Deutsch. Bot. Gesell., xxv. 24 (1907). 



