FIBRO- VASCULAR BUNDLES. 



101 



from the same ancestral cell ; hence every cell in the plant par- 

 takes more or less completely of the nature of every other cell. 

 The resemblances are primary and fundamental, the differences 

 secondary and derived. And what is 



true of the fern in this respect is v 



ro\ v // I// 

 equally true of all other many-celled \\] I /\ 



organisms. 



Course of the Fibro-vascular Bundles. 



Certain features of the disposition and 

 course of the fibre- vascular bundles in the 

 embryo and in the adult may conveniently 

 be studied at this point. From the point 

 of junction of the bundles of the first leaf 

 and first root (Figs. 67, 68, 69) is developed 

 one central bundle traversing the young 

 rhizome and sending branches into the new 

 leaves and roots until 7-9 leaves have been 

 formed. After this time the rhizome 

 forks, and the course of the fibro-vascular 

 bundles in each fork is henceforwards 

 compound. A lateral depression appears 

 in the central bundle of each stem, rap- 

 idly increases in depth, and soon divides 

 the bundle into two, one upper and one lower, which are best recognized 

 in old specimens (Fig. 35). When the forked shoots have reached a 

 length of about three inches, these bundles send out at a small angle 

 towards the periphery, thinner, forked branches which soon unite again 

 to form a network near the epidermis. The uppermost of these branches, 

 which, passes in the median line above the axile bundles, is usually some- 

 what more fully developed, and almost as broad as the latter. This 

 structure is generally retained in the mature rhizome (Fig. 35, x). The 

 number of peripheral bundles may be as great as twelve in the cross-sec- 

 tion. They anastomose in the vicinity of the place of insertion of each 

 frond, and thus form a hollow, cylindrical network, having elongated 

 meshes; but no connecting branches between them and the two axile 

 bundles are found anywhere in the rhizome. The latter follow an en- 

 tirely isolated course within the creeping stem;* branches from them enter 

 the leaves, and it is only inside the leaf-stalk that these ramifications are 

 met by branches from the peripheral network. The bundles of the roots 

 arise only from the peripheral bundles, but those of leaves, as already said, 

 receive branches from both axillary and peripheral bundles. Two thick 



FIG. 71. (After Sachs.) Young maid- 

 en-hair fern (Adiantum) attached 

 to the prothalliuin, p. I, leaf; 1, 2, 

 the first and second roots. 



* See, however, De Bary, Comp. Anat. Phanerogams and Ferns, p. 295. 

 Oxford, 1884. 



