FILICINEAR. —HOMOSPOROUS FILICINEAE. 



213 



Asplenitwi fiircatiim, for instance, frequently and in large numbers from the middle of 

 the upper surface of the laciniae, in Asplenuim deciissatum from the base of the pinnae 

 (or? they are axillary on the midrib), (Fig. 159); Ceratopteris thaliclroides produces 

 buds not unfrequently in all the angles of the divided leaves ; they arise at a very early 

 period from superficial cells of the leaf; if the leaf is cut off and laid on the damp 

 ground these buds develope rapidly and grow to strong plants. Long drooping 

 leaves of many Ferns with their extremities lying on the ground put forth roots 

 from them and sometimes new shoots, as in Chrysodiinn flagelliferum, Woodwardia, 

 and others. 



The growth of the leaf is strictly basifugal and apical, and this is followed by 

 further basifugal development. The stalk is first commenced, and the lamina begins 

 afterwards to show itself at its apex ; the lowest parts are first formed, the parts 

 above them in basifugal succession. The excessive slowness of this growth is very 

 remarkable and can only be paralleled in the Ophioglosseae. In older plants of 

 Pten's aqiiilina the leaf is begun fully two years before it unfolds ; by the beginning 

 of the second year the stalk, about one inch long and growing from an apical cell 

 which forms oblique walls in alternating directions, is the only portion yet in exist- 

 ence ; in the summer of the same year the lamina first arises on the apex of this 

 rod-like stalk, and is then a minute flat body concealed beneath the long hairs ; it 

 bends over with its tip downwards and hangs like an apron from the top of the stalk 

 (Fig. 160 B, C, D) ; it continues to grow beneath the ground and in the third spring 

 is raised above the ground by the elongation of the stalk, and has now only to 

 unfold. The whole of the leaves of a rosette of Aspidium Filix-mas take two years 

 to form; in their case also the leaf-stalk and the first rudiments of a lamina- on the 

 oldest leaves of the young rosette are produced in the first year. 



The basifugal growth at the apex of the lamina of the leaves of Ferns is most 

 remarkable, when it goes steadily on for a long time without arriving at a distinct 

 termination, while the lower parts of the lamina have long since been fully developed, 

 as happens in Nephrolepis. The periodical interruption to the growth of the lamina 

 at the apex, which has been already mentioned, occurs in many Gleichenieae and 

 Mertensieae, where the development of the leaves comes to a standstill above the first 

 pair of pinnae, and the interruption is repeated at the same place in the several orders 

 of branching when the pinnation is compound ; the consequence is that the tip of the 

 lamina appearing like a bud in the fork either remains always undeveloped, or 

 developes in like manner only imperfectly in a succeeding vegetative period ; it 

 appears that this intermittent mode of formation of the leaves may be continued 

 during a number of years ^. According to Mettenius the lamina of the leaf in many 

 of the Hymenophyllaceae is capable of indefinite growth and forms innovations every 

 year ; the primary branches also of the lamina of the leaf oi Lygodiiivi after the forma- 

 tion of each pair of pinnae of the second order remain in a bud-like condition at 

 their extremity, while the midrib grows indefinitely and looks like a twining 

 stem. 



The branching of the lamina of the leaves of Ferns in the developed state is not 

 unfrequently forked, as in Platyceritim, Schizaea, and others, but generally the leaf is 



Braun, Verjungung, 123. 



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Ju' 



