Metaphyta Pteris. 12$ 



of the annular cells. The contents of the sporangium are 

 thus ejected, If one of the spores be examined under a 

 high power of the microscope it will be found to consist of 

 a minute sac filled with granular protoplasm, with a nucleus- 

 The wall is differentiated into a thin inner 



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layer or endosporium, and a thick outer layer 

 or exosporium. 



Among the fertile sporangia are occa- 

 sionally to be seen barren sporangia, multi- 

 cellular club-shaped hairs which have been 

 termed paraphyses ; in other words, sporangia 

 which have not come to maturity, which have been crowded 

 out in fact, and have not had room to develop, owing to the 

 more vigorous growth of their neighbours. 



As already stated, the sporangium and its contents 

 are formed from the epidermal layer of the sporophyll. 

 Its mode of origin is of importance and demands a brief 

 description in passing. The sporangium first appears as a 

 bud from an epidermal cell on that region of the leaf to 

 which the name placenta has been given. The bud becomes 

 segmented off from the epidermal cell by a transverse par- 

 tition, just as is the case with multicellular or unicellular 

 epidermal hairs. Indeed, a sporangium in the primary 

 stages of its development is morphologically a hair or 

 trichome. The unicellular trichome segments transversely 

 into a proximal cell, which gives origin to the funicle, and a 

 distal cell which gives origin to the capsule. The proximal 

 cell segments repeatedly both transversely and longitud- 

 inally to form the funicle ; the distal cell also repeatedly 

 segments, but the details of segmentation are in that case of 

 more importance. In the first place four cells are cut off 

 tangentially, leaving the central cell to form what is known 

 as the archesporium. These tangentially formed cells be- 

 come the sporangial wall by repeated subdivision perpen- 

 dicular to the surface of the sporangium. The archesporium 

 next segments off again tangentially a layer of cells which 



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