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Elementary Biology. 



apparently in process of transformation into sperms. Simi- 

 larly when the so-called ripe macrospore is examined it is 

 found to consist of a very considerable collection of cells 

 enclosed in an endo- and exosporium, which latter has three 

 very well marked ridges on one surface. The cellular tissue 

 sho -vs more or less distinct demarcation into two areas ; the 



FIG. 62. STRUCTURE OF THE SPORES IN Selaginclla. (Pfeffer.) 



3 



i, 2, 3, ovospore of .$". martens IL A, D, spermospore of S. caulescens. 



upper of which, that is to say the part nearest the point of 

 union of the three ridges, is termed the thallus, whilst the 

 lower part has been termed the endosperm. In the thallus 

 are found three or four funnel-shaped depressions, leading 

 into minute cavities, which contain naked protoplasmic cells. 

 These cells are on further examination found to be com- 



