740 



LECTURE XLI. 



The other kind of orthotropic shoot, which comes forth into the da}light, makes 

 its appearance early in the spring, produces no chlorophyll, and has only the one 

 object of bringing to maturity the asexual spores produced long previously when 

 the shoot was still under ground, and to scatter them to the wind and so sow them. 

 These sporangiophores, which only attain a height of 20-30 cm., terminate above in 

 an ovoid or cylindrical ' fructification,' if one will so term it ; i. e. the apical portion 

 of the shoot-axis bears, in closely superposed whorls, numerous hexagonal shields 

 (metamorphosed leaves), fixed on slender horizontal stalks, and bearing on their 



Fig, 423. — Development of spores of Eqitisehtin 

 liinosnm (x 800). yl unripe spore witli three coats, fresh 

 and lying in water. B the same after lying for two 

 or three minutes in water : the outer coat has become 

 raised A large vacuole is seen near the nucleus. C 

 early stages in the development of the elaters on the 

 outer coat ^ (^ = i in Figs. .-/ and B), Z?, E similar stages 

 in optical section, after twelve hours in glycerine : e the 

 membrane whence the elaters are formed. 2 and 3 the 

 separated inner membranes. F the outer membrane split 

 into spiral elaters, which are coloured blue by chlor-zinc 

 iodine. 



Fig. t,-2s.—Equisetitm Tehnateia. A upper part of a fertile shoot with the lower half of the sporiferous spike 

 (nat. size) : b leaf-sheath ; a so-called ' annulus ' (bracts ; x the pedicel of sporangial leaves which have been re- 

 moved ; y transverse section of the axis. B peltate sporangi.al leaves in various positions (slightly magnified) : it 

 pedicel : s shield ; s^ sporangia. 



under-side (the one turned towards the axis) a large number of thin-walled delicate 

 sacs, the sporangia. These points will be rendered sufQciently intelligible, even 

 without detailed descriptions, from Fig. 422. The ripened sporangia dehisce, each 

 by means of a longitudinal fissure, and allow their spores to escape. It is only 

 necessary to tear off one of these sporangiophores in March or April and knock 

 the head on a plate, for instance, to obtain the spores in large quantities in the 

 form of an extremely fine greenish powder. On collecting this on a piece of 

 paper, for instance, and breathing lightly on it, an agitating writhing movement 

 is noticed in it : this is still more obvious when the same experiment is made 

 with a few spores on a glass slip under the microscope, with a low power. It 



