ANCYLISTALES 



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strictions at the septa are usually not present. The resulting 

 cells differ in size and form, and some of them may be slightly 

 branched. As in Myzocytium the component cells of the thallus 

 may function either as sporangia or sexual cells, but here the 

 male and female gametangia may occur on the same or on differ- 

 ent thalU. In some species {e.g., L. entophijtum) male cells are 

 not differentiated, the "oospores" being developed without 

 fertiUzation (parthenogenetically). The germination of these 

 spores has not yet been observed. The classical figures of Zopf 

 (1884: pi. 1-3) picture the various steps in the life cycle in two 

 species of the genus. According to his account and those of other 

 early students the sporangium germinates by the emission of 



Fig. 46.- — Lagenidium amcricanum Atkinson in zygospores of Spirogyra. 

 (a, b) Sporangia, some emptied, {c-h} Stages in swarmspore formation. 

 {After Atkinson 1909.) 



the contents into a bladder at the mouth of the exit tube, the 

 swarmspores being delimited in the bladder. Atkinson 

 (1909: 330) after studying two species, including one of those 

 figured by Zopf, states that, in fact, a bladder is not formed. 

 According to his account the protoplasm escapes from the tip 

 of the tube as a naked mass and though usually remaining at the 

 mouth in the form of a ball sometimes breaks away as a detached 

 sphere. In a few moments a rotary motion begins, and the 

 swarmspores are gradually delimited and escape one by one from 

 the moving mass. The details of the process are described at 

 some length and in an interesting manner. To the writer it 

 seems likely that the bladder is sometimes present and that at 

 other times the tip of the exit tube ruptures before it forms. It 

 would seem that too much emphasis has been placed on the 



