THE DEVELOPMENT OF DUMONTIA 275 



the resting state. It was then thought that the failure to find 

 mitosis might be due to the fact that the collections were not 

 made in twenty-four consecutive hours and that the plants were 

 not taken from the same gi'oup in a tide pool or even from the 

 same tide pool. Thus, if mitosis regularly occurs at a certain 

 hour of the night, a change in the intensity of the light of the 

 proceeding day or a change in temperature may so alter the 

 physiological conditions in the plant that the nucleus will divide 

 one or two hours earlier or later than the usual time. The 

 collections in this first series were made on seven different days 

 and it is quite possible that the hour at which mitosis occurred 

 varied somewhat during this time. 



A second series of collections was then made. This collec- 

 tion was made during the greatest of a series of spring tides. 

 Five or six plants were fixed at each hour in Flemming's medium 

 chrom-acetic-osmic mixture. It took about fifteen minutes to 

 cut the plants, hence the time elapsing between the successive 

 fixations was about forty-five minutes. The plants were gath- 

 ered from certain groups in three different tide pools. In six 

 collections which were made at high tide, it was impossible to 

 reach these pools; so the stones on which some of the plants in 

 these groups were growdng were for this length of time placed 

 in an artificial tide pool near the shore. The plants cannot be 

 considered as having been placed in abnormal conditions, be- 

 cause even in this artificial tide pool they were covered by as 

 much water and as much exposed to the surf as they were for at 

 least half of the month, in the tide pools in which they grew. 



As will be shown later, even from this material very few data 

 were obtained concerning mitosis. Hundreds of tetrasporangia 

 were examined in the material of each of these twenty-four 

 collections. It is very evident that the mitosis occurring in the 

 tetrasporangium nucleus of Dumo7itia must be of exceedingly 

 short duration. In the material collected at 9:00 a.m., a few 

 stages of nuclear di\dsion were found. Several tetrasporangia 

 which were one-celled but binucleate were also seen. Since 

 nuclear division in the tetrasporic plants is always immediately 

 followed by cell division, the occurrence of the unicellular, 



