386 



VASCULAR CRYPTOGAMS. 



The protliallium o{ Sahnnia fuitam^ attains a much more considerable size than 

 that of the two other genera ah-eady mentioned ; it is destitute of chlorophyll, and 

 forms a number (which may even be large) of archegonia in definite positions. 

 After it has broken through the membrane of the papilla, it appears seen from 

 above, as three-sided between the three torn lobes of the exospore ; one of these 

 sides is anterior ; the two posterior sides meet behind at an acute angle ; a line from 

 this angle to the centre of the anterior side runs above the elevated saddle-shaped 

 back of the prothallium, and forms its median line. The anterior side projects above 

 the back, and, where it meets the two posterior sides, the two angles grow subse- 

 quently into long wing like prolongations .hanging down by the sides of the 

 macrospore. The first archegonium makes its appearance on the median Hne of 

 the elevated back immediately behind the growing anterior side of the prothallium ; 



KIG 2R7. — Salvinia 7iafa)t<r (after Pringslieiin). A longitudinal section through tlie macrospore, prothallium, and ' 



embryo in the median line of the prothallium (X about 70), a layer of cells oj]^ the sporangium, b exospore, c endospore, 

 e its prolongation, d the diaphragm mentioned above which separates the prothallium from the spore-cavity, /r the pro- 

 thallium already broken through by the embryo, /, // its two first leaves, s the scutiform leaf; B an older seedling with the 

 spores/ and prothallium /;-{X 20), a the pedicel, b the scutiform leaf, /, // first and second single leaves,/., L' aerial leaves 

 of the first whorl, iv submerged'leaf of the first whorl. 



tVk^o other archegonia then invariably appear right and left of the first, so that they 

 'Stand in a transverse row parallel to the anterior side. If one of these archegonia 

 is fertilised there is an end of the growth of the prothallium ; but if this does not 

 happen, the prothallium continues to grow on its anterior side, and from i to 3 new 

 transverse rows of archegonia are produced, each of which contains from 3 to 7. 

 The long central cell of each archegonium lies obliquely in the tissue of the pro- 

 thallium, so that the outer (neck) end faces backwards, its inner deeper end facing 

 the anterior surface. At this latter point lies at a subsequent period the apical 

 cell of the embryonal stem. Young archegonia have the apex of their central cell 



^ All that is said about Salvinia is from Pringsheim, /. 



