198 



INTRODUCTION TO CYTOLOGY 



biciliate in Ulothrix, laterally biciliate in Ectocarpus, and crowned with a 

 ring of many cilia in (Edogonium. Non-motile spores (aplanospores) 

 also occur in some genera. In Polysiphonia, carpospores are budded off 

 from the carpogonium and tetraspores are formed in groups of four in 

 the tetrasporangium. In some algae, notably Spirogyra and its relatives, 

 the product of gametic fusion is a resting zygospore. 



The cytological phenomena appear to be about the same in the devel- 

 opment of motile gametes and spores of a given type. The protoplasm 

 of the antheridium or the sporangium, as the case may be, is often not 

 entirely used up in the formation of the spermatozoids or zoospores. 

 The chromatophores, if large and continuous, ordinarily break up into 

 numerous smaller ones, while the pyrenoids and starch tend to disappear 

 as the gamete or spore primordia are delimited. In each primordium 



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FiG. 115. — Development of blepharoplast in (Edogonium. (After Kretschmer, 1930.) 



there are differentiated an eyespot and a motor apparatus, the latter 

 consisting of a blepharoplast with its attached cilia. 



The development of the blepharoplast, or cilia-bearing organ, has 

 attracted much attention in these and other organisms. In CEdogonium 

 (Fig. 115) the nucleus moves against the cell membrane, which there 

 forms a convex thickening. In the plane of contact there appears a 

 ring of granules. As the nucleus loses contact with the thickening the 

 ring becomes double, and from its outer half a crown of cilia grows out,* 

 Each of the many pairs of cilia on the coenocytic Vaucheria swarm spore 

 is in some way associated with a nucleus lying near the cell membrane. 

 In Eudorina the pointed end of the nucleus, to which a centriole is 

 attached, touches the membrane and then retreats to the center of the 

 cell, leaving behind a double body (centrioles?) from which the cilia grow 

 out (Hartmann, 1921). Such blepharoplasts as that of CEdogonium are 

 called " plasmodermal blepharoplasts" to distinguish them from the 

 "centrosomal blepharoplasts" of pteridophytes, bryophytes, and some 

 of the lower forms. 



* Strasburger (1892, 1900a), Kretschmer (1930). 



