474 MOSSES AND FERNS chap. 



peripheral portion made up of parenchyma, with a circle of 

 scattered narrow sieve -tubes. A definite endodermis cannot 

 be demonstrated. In the species with the leaves all alike both 

 surfaces bear stomata, but in those with decussate leaves the 

 greater part of the upper surface is destitute of them. 



The Root 



The roots of Lycopodium arise, as in other Pteridophytes, in 

 acropetal succession, but with no relation to the position of 

 the other organs. According to Bruchmann adventive roots 

 may arise in L. inundatum, but they have not been observed 

 in other forms. L. selago ^ may serve to show the characters 

 of the root in the genus. The meristem of the apex is clearly 

 differentiated into the initials of the different primary tissues 

 (Fig. 247, C). The dermatogen [d) completely covers the apex 

 of the growing point as a single layer. The periblem {j)U) is 

 three cells thick ; the plerome (//) terminates in a group of 

 special initials. As in the stem, the plerome alone forms the 

 central cylinder, the periblem giving rise only to the cortex, 

 and the structure of the mature root corresponds closely to 

 that of the stem, except for the presence of the root-cap, which 

 has its own initial group of cells (calyptrogen, cat). From the 

 older dermatogen cells are derived, by special walls, the mother 

 cells of the root-hairs (Ji). 



Van Tieghem ^ states that the secondary roots arise from 

 the pericycle instead of from the endodermis, as in other 

 Pteridophytes, but Strasburger claims that the so-called peri- 

 cycle of Lycopodium is really cortical, and does not belong 

 properly to the central cylinder, so that this difference is only 

 apparent. The endodermis itself is not readily recognisable 

 on account of the complete cutinisation of the walls. 



The origin of the root-hairs is somewhat peculiar. From 

 the base of each dermatogen cell a wedge-shaped cell is cut 

 off (Fig. 247, C, Ji), and this afterwards is divided into two 

 similar cells, each of which grows out into a unicellular hair. 

 Thus the root-hairs are found in pairs. 



The roots always normally branch dichotomously, as in 

 Isoetes, and the successive divisions usually are in planes at 

 right angles to each other. " As in Isoetes, the process is in- 



^ Strasburger (10), p. 259. ^ Van Tieghem (5), p. 553. 



