330 



I'LANT STl'DIKS 



All onliuury 

 itnd ;t Ijiilliuiis 



U^'l 



«u. 



n 



Fl(i.3n0. A nionnwort 

 ^Biil n/rltiinn)^ show- 

 ing thi- 1 ciifdiHcvelit i- 

 ated into foliugi.' and 

 sporophyll ])ranc!ics. 

 —After STiiAsiuru- 



GEK. 



unless it l)c tli 

 here. 



f(_'i-ii sporuii,i;-ium c()iisists of a slender stalk 

 to}) which is the spore case (Fig. 290, (J). 

 Tliis case has a delicate wall formed of 

 a single layer of cells, and extending 

 around it from the stalk and nearly to 

 the stalk again, like a meridian line aliout 

 a glohe, is a row of iieeiiliar cells with 

 thick walls, forming a. heavy ring, called 

 the a It// /f/ IIS. The annnlas is like a hent 

 s})ring, and when the delicate wall he- 

 comes yielding tlie spring straightens 

 violently, the wall is torn, and the S2)0res 

 ai'e dischai'ged with considerahle f<.)rce 

 (Fig. oOl ). This dis(diarge of fern spores 

 m;iy he seen hy j)lacing some sporangia 

 upon a moist slide, and under a low 

 power watching them as they dry and 

 hurst. 



21.'). Heterospory. — This phenomenon 

 a}ipears hrst among Ptcridophytes, hut it 

 is not characteristic of them, hcing en- 

 tirely ahsent from tlie true Ferns, which 

 far outnumher all other Ptcridophytes. 

 Its chief interest lit^s in the fact that it 

 is universal a.niong the Spcrnuitophytes, 

 a,nd that it represents the change which 

 leads to tlie ajipearance of that high 

 group. It is impossil)le to understand 

 the greatest group of jilants, therefore, 

 without knowing something ahout heter- 

 ospory. As it hegins in sim]ile fasliion 

 a.niong Ptcridophytes, and is prol)al)ly 

 the greatest contrihution they have made 

 to the evolution of the plant kingdom, 

 e leafy sporophytc, it is hest exphiincd 



