CHAPTER IV 



MORPHOLOGICAL ANALYSIS OF THE SHOOT- 

 SYSTEM OF FERNS 



The sporophyte of modern Ferns, however complex, is built up on the basis 

 of the simple shoot, constructed on essentially the same plan as that of the 

 Higher Vascular Plants. The differences are those of detail rather than of 

 principle. The Shoot consists of an axis terminating in a growing point 

 endowed with unlimited powers of development, which bears leaves as lateral 

 appendages produced exogenously upon it, and in acropetal order. This shoot 

 is fixed in the soil by roots which are of adventitious origin, and variable in 

 number. Though they may at times show some degree 

 of regularity both in number and in position relatively 

 to the leaves, this is by no means a general rule. Never- 

 theless a frequent relation is such that one root arises 

 immediately at the base of each leaf This is well seen 

 in Ophioglossinn vulgatum, and in Bleclumvi Patersoni 

 (Fig. 57). 



As has been seen in Chapter II, the position of the 

 axis may be erect, ascending, or prone. Closely con- 

 nected with the pose of the shoot is its symmetry. In 

 Ferns as in other plants a shoot directed vertically 

 upwards is usually radial, while ascending or creeping 

 shoots show varying degrees of dorsiventrality, the 

 difference of symmetry being referred to the effect of 

 gravity upon it. The same question of priority will then 

 arise regarding the radial and dorsiventral symmetry as 

 for the erect and prone positions. In Vascular Plants at 

 large there is a strong probability of the erect position 

 and radial S3'mmetry having been primitive in the sporophyte, and the prone 

 position and dorsiventral symmetry derivative. The analogies between Ferns 

 and other Vascular Plants in this respect are so close as to justify a similar 

 conclusion for their adult shoots, and it would apply to the juvenile shoots 

 also in the most primitive Ferns, such as the Marattiaceae and Ophioglos- 

 saceae, where the embryo is erect from the first. But the prone position of 

 the Leptosporangiate embryo presents a difficulty in accepting the conclu- 

 sion as general for all Ferns. Moreover the relation of the symmetry of the 

 shoot to gravity is not always so simple and direct as it usually appears to 



Fig. 57. Blechinim Pa- 

 lersoni (R. Br.), Mett. 

 Tangential section of 

 the stock, showing a 

 constant relation of 

 one root below each 

 leaf-trace. ( x 6. ) 



