BKYUl'llYTES 101 



Thallophytes. Instead of being a single mother cell, it is 

 a many-cellud structure, shaped like a flask (Figs. 83, 98). 

 The neck of the flask is more or less elongated, and within 

 the bulbous base {venter) the single egg is organized. The 

 archegonium, made up of neck and venter, consists mostly 

 of a single layer of cells. This hollow flask is solid at first, 

 there being a central vertical row of cells surrounded by 

 the single layer just referred to. All of the cells of this 

 axial row, except the lowest one, disorganize and leave a 

 passageway down through the neck. The lowest one of 

 the row, which lies in the venter of the archegonium, or- 

 ganizes the egg. In this way there is formed in the arche- 

 gonium an open passageway through the neck to the egg 

 lying in the venter. 



To this neck the swimming sperms are attracted, enter 

 and pass down it, one of them fuses with the egg, and this 

 act of fertilization results in an oospore. 



It is supposed that archegonia have been derived in some 

 way from oogonia, but no intermediate stages suggest the 

 steps. In any event, the presence of the archegonia is one 

 strong and unvarying distinction between Thallophytes 

 and Bryophytes. Pteridophytes also have archegonia, and 

 so characteristic an organ is it that Bryophytes and Pteri- 

 dophytes are spoken of together as Archegoniates. 



65. Germination of the oospore. — The oospore in Bryo- 

 phytes is not a resting spore, but germinates immediately 

 by cell division, forming the sporophyte embryo, which 

 presently develops into the mature sporophyte (Fig. 85, A). 

 The lower part of the embryo develops downward into the 

 gametophore, forming the foot, which penetrates and ob- 

 tains a firm anchorage in the gametophore (Fig. 85, B, 0). 

 The upper part of the embryo develops upward, organizing 

 the seta and capsule. In true Mosses, when the embryo 

 becomes too large for the venter of the archegonium in 

 which it is developing, the archegonium is broken near the 

 base of the venter and is carried upward perched on the top 

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