MARSILIA 



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gametophijtes, developed by the microspores; and (2) female 

 gametophytes, developed by the megaspores. The differentiation 

 of spores into two sizes, microspores and megaspores, which 

 develop respectively male and female gametophytes, is called 

 heterospory. 



D. The male gametophyte. This small structure can best be 

 studied by means of microtome sections (see Principhs, 

 Fig. 282, A). Living material will, however, show the rup- 

 tured microspore, a protruding cellular papilla, and, at the 

 proper stage, developing sj^erms within. Draw such germi- 

 nating spores. 



1. Sjjerms are generally to be found swimming about in the 

 water, especially in the vicinity of megaspores, which by 

 this time have developed archegonia, formed singly at one 

 end of the spore. Excretions from the archegonium exert 

 an attractive influence, called chemotaxis, upon the sperms. 



2. Stain the sperms with iodine. Note the spiral body, like 

 a long corkscrew, and the numerous cilia distributed 

 over it. A vesicle, frequently to be found at the larger 

 end of the spiral, is the remains of the sperm mother cell. 

 Draw the stained sperms. 



E. The female gametophyte. This consists of a short-necked 

 archegonium developed at the end of the megaspore, which 

 was marked by the slight protuberance. Microtome sections 

 are necessary to show its detailed structure (see Frinciples, 

 Fig. 282, C). In the living material note and show in a figure : 



1. The opening into the short neck. 



2. The arrangement of sZme around the archegonium end 

 of the megaspore in which sperms are frequently caught. 



3. The swollen base of the archegonium containing the egg. 



Note the relatively small amount of chlorophyll in the 

 cells of the female gametophyte. Where does it get the 

 food necessary for its development ? 



F. The young sjyorophyte. The sporophyte begins to develop 

 at once from the fertilized egg. The early stages of its 



