FER\-I'I,()HA OF c: AN A DA. 



225 



The Rachis and its side Branches or Rachides ; Veins ; Veinules ; 



Veinlets. 



As tlie ooiuiiuiiitioii of the i^/i/)i>. into u dividtnl or compound frond-lauiina is 

 Oidlod tlu; Rar/iis, and its side hranches Seromfari/ ll'trldtleKy so, \vli(;n ll»e laniinii 

 is simple or undivided, the midvein (in that case also a continuation of the stipe) 

 is called the Co^fa or midrib. Tht; ditlerent modes in which the veins, formin<i[ 

 the framework of the leafy i)ort>on of the frond are disposed ati'ord useful ciiarae- 

 ters in the discrimination of species ; the hranehes from the costa are teitntid 

 VcJm : the brancln's from tlie.-e veins are called Vfimih'x, and tlu! braricdies (»f 

 the veinules, Velnleti^. In like manner, whatever may 1)h tlu; extent of division 

 of a frond into pinnae or lobes, tiie V inn are the first series of liranches from the 

 midrib or costa (whether of the frond when simple, or of its separate ultimate 

 divisions, or leaflets, when compound). V'i'Iha are the t)rimary branches from tlu! 

 costa, Veinnleti the secondary, and Vi'inlcts the t".rtiaiy aeri(!s. \Vh(>re there is 

 no prominent costa, the ribs arising directly from the base of the leaflet are called 

 veins. The part of the vein on which tlu; fruit dot ov Sof/is is seated, is called 

 the Reccpfade. 



The jiarts described may all be seen, more or less distinctly, by the naked eye, 

 but, in examining tlu; veining of the fron<ls, the sorus or fruit dot, and its jirotect- 

 ing indusium, a simple lens or magnifying glass of any kind will give great help. 



Tub 80RUH, OK Khuit Dot. — The sorus (plural xori) will be seen to consist of 

 numerous visor shojied, usually stalked, pouches, called Spure-Caxes^ each filled with 

 an exceedingly fine dust ; the individu d particles of this dust, c died S/jores, are too 

 minute to be visible even to the keenest human eye, without a lens, yet it is these 

 tiny particles that give rise (as if they were buds or seeds) to new individual plants. 

 The remarkable proceses attending the growth and development of these invisible 

 specks into fern plants can oidy be followed Ijy use of the compound microscope. 



Thk Indusium. — In some ferns (as the common [)oly[)ody and the oik f(U'n) 

 the sori are simply round granular dots of S[)ore cases, without any protective; 

 covering ; in many others, the little clusters of spore cases are enveloped or 

 sheathed at first in a delicate, colourless, scaledike membrane, or are surmounted 

 by a small disc or shield-like covering. This protecting organ, which falls away 

 as tlie spore cases mature and drop their spores, is called the Indusiuuj. 





