244 



PLANT STUDIES 



and cut off from the general cavity by partition walls (Fig. 

 210). The oogonium becomes a globular cell, which usually 



Fig. 210. Vayrht-ria ^es.^'/lh. a Siphon fnrm, 

 showing a portion of the ca-nocytic lioilv, an 

 antheridial hraiich {.4) with an empty an tln.'- 

 ridinm ia) at its tip; and an oogonium {]>) 

 containing an oospore ic) and showing tlte 

 opening (/) through which the sperms passed 

 to reach the egLr. — Caldwell. 



develops a perforated break for 

 the entrance of the si)erms, and 

 organizes within itself a single 

 large egg (Fig. 210, B). The an- 

 theridium is a much smaller cell, 

 within which numerous very small 

 sperms are formed (Fig. 210, A,i(). 

 The sjierms are discharged, swtirm 

 about tire oogonium, and finally 

 one passes tlirough the break and 

 fuses with tlio egg, the residt lie- 

 ing an oospore. The oospore or- 

 ganizes a thick wall and becomes 

 a resting spore. 



It is evident that V((uc]ii'riii is hetcrogamous, but till 

 the other Sijihon forms are isogamoiis, of which Btilnidiiim 

 may be taken as tin illustration (Fig. 211). 



1(17. Spirogyra.— This is one of the commonest of the 

 "pond scums," occurring in slippery and often frotliy 

 masses of delicate filaments llotiting in still water or about 



, ^11. JUttryd'vnii, one of 

 tile Siplion forms of green 

 ali:;p, tlie whole body con- 

 taining one eoiitinnons cav- 

 ity, \:itli a Inillious, ehioro- 

 jiliyll -ecuitaining ])ortion, 

 and root-iilic liranches 

 wliieh jienetrate the mud 

 in wliieli the i)Iaiit gro\\s. 

 — Caldwkll. 



