SPORANGIOPHORES, ETC. OF EQUISETUM. 



741 



is then observed ihat each individual spore is a sj)hcrical cell provided with a thin 

 tough membrane and with protoi)lasm containing chlorophyll, and has two mutually 

 crossing long bands attached to it at one point (;/, Fig. 423 A,B). When 

 the air is dry these crossed bands are thrown widely apart ; but it suffices while 

 looking through the microscope to simply breathe lightly, and thus supply the 

 spores with damp air, to put the bands in motion at once, and they then roll 

 themselves together round the spore with extraordinary ra])i(lity, as in Fig. 423/'', 

 energetically opening out again at once when 

 the small quantity of moisture hygroscopically 

 absorbed evaporates. These movements of 

 the ' elaters ' take place so energetically and 

 rapidly that the spores are put into jumping 

 movements, which will evidently also occur in 

 the open as the moisture of the air changes, 

 and may in some way contribute to bring the 

 spores into suitable places for germination. 



The sporangiophores of the above Equi- 

 sctum disappear after the sowing of the 

 spores ; other species, however (e. g. ^. //mo- 

 si/m, which sometimes completely fills up 

 large swamps) send up shoots of one kind 

 only above the soil, which contain chloro- 

 phyll, and bear the spikes of sporangia at 

 the apex at the same time. 



The whole of the Equisetum- plant so 

 far described is devoid of sexual organs ; the 

 only reproductive organs it produces are the 

 sporangia described. The whole plant is 

 thus quite asexual, and this holds good not 

 only of the Horse-tails, but in exactly the 

 same way of the Ferns and Lycopodiaceos 

 and Selaginellse, &c. In all these cases the 

 ordinary, long-lived and sometimes (as in 

 the case of Tree-ferns and extinct Lepido- 

 dendrd) huge tree-like plant is asexual ; it 

 always produces as reproductive organs spo- 

 rangia only. 



If now the spores of the Florse-tail are sown on the surface of water, for 

 instance, on which they float, an opportunity is easily affortled of observing their 

 early stages of germination. These are represented in Fig. 424. In / and 

 // the germinating spore is seen to be in the first place segmented into root 

 (7V) and shoot (/); the root, a simple utricle, turns geotropically downwards, 

 while the shoot containing chlorophyll (/) floats on the water and undergoes 

 numerous successive cell-divisions. Germinating on ordinary water, however, the 

 plantlets usually develope no further than in Fig. 424 VI \ they attain their complete 

 development, however, if the spores are sown on loamy soil or on the surface 



Fig. 424.— First stages in tile 

 development of the prothalliuni of 

 Iiquisettitn TehttaUia : w first root- 

 hair; t incipient shoot. The de- 

 velopment is in the order of the 

 numbers I— VI (X about 200). 



