INTRODUCTION 9 



is used to form a membrane, the peridium, over the surface of 

 the sporangium. Similarly, as the protoplasm passes into the 

 sporangia other waste materials are often left behind on the 

 substratum and may form a glistening film, termed the hypo- 

 thallus. Within the sporangium Unes of cleavage cut the proto- 

 plasm into progressively smaller portions until finally uninucleate 

 bits are delimited. Each of these secretes a definite wall, and 

 develops into a globose spore. During the process of protoplasmic 

 cleavage, waste materials not used in the formation of the 

 peridium are deposited in elongate vacuoles, and form there 

 cylindrical threads called capillitium. These threads are often 

 ornamented with beautiful surface markings, spiral thickenings, 

 spines, etc., which afford characters of diagnostic value useful in 

 generic separation. At maturity the peridium bursts or disinte- 

 grates, and the mass of capillitium and spores is exposed. The 

 spores then fall out and are disseminated by the wind. 



The name Myxogastres was selected as indicative of the 

 marked resemblance which certain of these organisms show to 

 the Gastromycetes. The similarity is, however, only superficial. 

 The capilUtium and peridium in the Gastromycetes are formed 

 from hyphae, made up of living cells, and are consequently wholly 

 unlike the structures bearing the same names in this group. 



Nuclear division in the Myxomycetes has been studied in 

 various genera, and seems to be essentially a typical mitosis. 

 No evidence of the existence in the group of a primitive type of 

 mitosis resembling that of the Plasmodiophoraceae has been 

 found. In Ceratiomyxa, sole representative of the Exosporeae, 

 OHve (1907) states that a sexual fusion of nuclei in pairs occurs 

 just preceding the cutting out of the young uninucleate spores. 

 He says that this is followed immediately by synapsis and the 

 reduction divisions, the matures pores being quadrinucleate. 

 Jahn (1907) in a study of the same species found fusion and 

 reduction at a much earlier stage. A reinvestigation of this 

 form and a comparison of the nuclear history here with that 

 in various members of the Myxogastres is desirable. Until we 

 know more concerning sexuality and nuclear phenomena in the 

 group we cannot arrive at any safe conclusion concerning its 

 relationships with other lower forms. 



Acrasieae. — The Acrasieae comprise a small group of sapro- 

 phytic, and for the most part coprophilous organisms, lying 

 apparently at the extreme lower Umit of the plant world. They 



