DEVELOPMENT OF THE OSTRICH FERN. ' 29 



in other ferns at the same stage, and this corresponds with the comi^aratively late appear- 

 ance of the first cap-cell ; but it was not uncommon to find specimens, in which the root 

 has attained considerable size at this time, and indeed is the first part to break through 

 the prothallium. The root-cap in such cases is composed of several strata, and the first 

 cap-cell must have been formed much eai-lier. 



Shortly before the embryo breaks through the prothallium, the first traces of the pri- 

 mary fibro-vascular bundles are formed (PI. 6, fig. 2). In the central row of cells, in 

 each of the four members of the embryo, is formed almost simultaneously, a series of 

 longitudinal walls, by which there is formed a central bundle of narrow cells, the pro- 

 cambium of the bundles; hence the primary fibro-vascular bundles must be regarded as 

 distinct, and entirely independent of each other. Of these four bundles, that of the foot 

 is short, and ends blindly within that organ, but the others continue to lengthen with the 

 growth of the organ to which they belong, and shortly after the breaking through of 

 the embryo, the permanent elements of the bundle begin to develop. The stem grows 

 slowly, but the leaf and root with great rapidity; the former, even before the emergence 

 of the embryo, being evidently two-lobed. The apical cells of these lobes also undergo 

 bipartition, so that all the divisions of the primary frond are the result of strict dichot- 

 omy. Small glandular hairs appear upon the young leaf, and root-hairs from the surface 

 cells of the root, even before any definite ejjidermis can be detected. The root rapidly 

 grows downward, the first leaf enlarges and the prothallium, which had hitherto nour- 

 ished it, withers away and disappears leaving the yonng j'lant firmly fastened to the 

 ground. 



The primary bundles are arranged like a cross, two of the arms being longer. The 

 longer arras are the bundles of the leaf and root. The first tracheary tissue begins to form 

 about the time that the embryo breaks through the prothallium. Faint thickenings 

 make their appearance on the walls of certain of the procambium cells which soon as- 

 sume the form of scalariform tracheids. The pits are shorter than in the later tracheids, 

 and there are usually two or three rows. There are no true vessels, the tracheary tissue 

 consisting throughout of single cells or tracheids. 



As the leaf-stalk lengthens, its primary ti-acheids continue to form through the center 

 of the bundle, and around them other spiral ones are developed, growth proceeding from 

 the center toward the circumference of the bundle. The other elements of the bundle 

 follow, but are never perfectly difierentiated, consisting simplyof elongated, narrow cells 

 with thin walls and colorless contents. These do not taper at the ends but are abruptly 

 truncate, the septa being more or less oblique. The same form of bundle is found in all 

 the earlier leaves, none but spiral tracheids being found in them. The later ti'acheids 

 are broader than the primary ones and the spirals not so close together. Although there 

 is no distinct bundle-sheath, the bundles are pretty well defined on account of the 

 large size of the cells of the surrounding parenchyma, which are verydift'erent from the 

 narrow cambiform outer cells of the bundle. 



As might be expected, the veining of the leaf is dichotomous. The bundle in the stalk 

 forks at the base of the lamina, sending a branch to each lobe; these branches fork, and 

 their divisions also; the last veins thus formed may or may not divide once more. 



In the first root, the primary tracheids are central, as in the leaf, and the development 



