324 REPRODUCTION OF EQUISETUM 



ends, attached to the spore at one point (Fig. 234, 3). These 

 bands or elaters are very hygroscopic and their movements assist 

 in rupturing the sporangium, but their special significance is seen 

 in the fact that the elaters become entangled and so several spores 

 are carried away together by the wind. The meaning of this 

 arrangement will appear directly. 



(c) Germination of the Spore. — The gametophyte produced 

 from these spores (Fig. 235) is an irregularly lobed thallus more 

 suggestive of the irregular thallus of an hepatic or the leaves 

 of a moss plant, or the lobed gametophyte of certain species of 

 the Ophioglossales than of the prothalHum of the Filicales. The 

 most important feature about the gametophytes is the fact that 

 they are as a rule dioecious and of two sizes, the smaller ones 

 bearing only antheridia and the larger only archegonia. This 

 difference in the nature of the gametophytes is largely due to 

 nutrition as noted among the Filicales, the well-nourished ones 

 being the female. In fact antheridia may appear upon the female 

 gametophyte as a result of insufficient nourishment during its 

 later development. Thus we see that the germination of these 

 spores, which are apparently exactly alike, is controlled by a defi- 

 nite stimulus, just as was the case in the formation of zoospores 

 and gametes among the lower green algae (page 174). It is 

 noteworthy that some of the extinct species of this group actually 

 stored more food in certain spores than in others, so that they 

 came to differ somewhat in size. This habit is well established 

 in some of the living Filicales and will also be noted in the next 

 order. As a consequence of this tendency, the nature of the 

 gametophyte developed from the spore is no longer a matter of 

 chance. The larger spores, called megaspores, by reason of the 

 more abundant food produce female gametophytes, while the 

 smaller spores, microspores, form small gametophytes bearing 

 only antheridia. The significance of this tendency to produce 

 megaspores and microspores will be seen in the discussion of the 

 fourth order, but attention is called to it here because the Equise- 

 tales show very clearly how such a condition came about. It 

 would appear probable that the spores of Eqiiisetum, although 

 exactly alike as far as we can see, must have already undergone 



