520 



HUTCHINSON'S POPULAR BOTANY 



fills the greater portion of the spore is being converted into a cellular 

 tissue variously designated the secondary prothallium and endosperm. The 

 archegones are produced on the surface of the prothallium, some of them 

 being already present when the latter is extruded from the megaspore. 

 There is a neck with its canal leading to the interior with its oosphere. 

 The microspores are coloured red or orange, <\nd although development 



begins in the sporangia through- 

 out the winter, they appear to 

 make no advance upon their con- 

 dition when set free. In spring, 

 however, fresh activity is mani- 

 fested, and one portion of the proto- 

 plasm becomes an antherid, some 

 of whose numerous cells contain 

 coiled antherozoids with two long 

 cilia attached to the tapering fore- 

 part. For half an hour or so after 

 the rupture of the mother-cells the 

 antherozoids are endowed with 

 motion, and find their way by the 

 neck canal to the oosphere. Thus 

 fertilized, the oosphere develops 

 into an embryo with a pair of 

 primary leaves, a root, and a foot 

 or organ of absorption. 



The Prickly Club Moss (Sdn- 

 ginella selaginoides] is found in 

 swampy situations, chiefly on moun- 

 tain-sides, not farther south than 

 Wales. Its slender stem is not more 

 than six inches in length. It creeps 

 along the ground, but the fertile 

 branches which bear the sporanges 

 rise erectly, and end in a cone with 

 larger leaves (sporophylls). 



The genus Isoetes is represented 

 in this country by a single species, the Quilhvort (Isoetes lacustr'ts}. Though 

 the plants of Quillwort and Selaginella are as unlike as possible, the 

 developmental history of the embryo is very similar to what we have 

 just described. The Quillwort grows at the bottom of lakes among the 

 mountains of the northern half of Britain, and its stem takes the form of a 

 corm whose increase is not so much in length as in diameter. The leaves are 

 awl-shaped, with broad overlapping bases which entirely hide the corm 

 and in which the sporanges are produced. The outer leaves bear mega- 



FIG. 663. HAIR Moss (Polytrichum 



commune). 



(aa) Antheridia. (bb) Hairs and sterile filaments 

 (paraphyses). 



