239 



Among Ihe distinctive characters of this species, used hy Rosanokf, in his 

 important paper on the Melobesiacese, the want of "heterocysts" has been of special 

 importance in distinguishing it from M. farinosu, as it permitted determination even 

 in cases where the characters talvcn from the organs of reproduction could not be 

 used. As shown by Foslie however, 1. c. p. 103, the cells situated under the dicho- 

 tomies are often larger than the others and resemble the heterocysts of M. farinosa. 

 I can conlirm Foslies' statement, having frequently found these cells in Danish 

 specimens of M. Le- 

 jolisii. They agree 

 indeed completely 

 with the hetero- 

 cysts of M. farinosa, 

 in bearing a hair 

 or a scar left by 

 a shed hair, in 

 being poorer in 

 contents and in 

 bearing no cortical 

 cells as do the other 

 cells of the mono- 

 slromatic frond. 

 But they differ 

 from the hetero- 

 cysts of the last- 

 named species in 

 being derived, not 

 from end-cells of 

 filaments, which 

 do not develop 

 further, but from 

 cells situated under 



a ramification. I have convinced myself that this difference really exists by exami- 

 ning authentic specimens of M. farinosa. Where the included heterocysts of this 

 species are present it is easily seen that the two cell-rows, the separating line of 

 which goes in continuation of the heterocyst, are not given off from this, but from 

 the adjacent cell-rows. As shown by Solms (Cor. p. 24), these cells produce a hair 

 without formation of a transverse wall. The hairs are, according to the mentioned 

 author, very short-lived, and fall off after a separation has taken place at their base 

 by local incrassation of the longitudinal wall. This is also the case with those of 

 M. Lejolisii ; sometimes, however, they are more persistent, and appear as long 

 hyaline hairs (fig. 156 C). Their wall is stained very intensely by ha^matoxyline, 

 by which they become very obvious, and the same is the case with the basal part 



Fig. 156. 



Melobesia Lejolisii. from Biikholni, Sf. ,1, vertical section oC marginal part ol frond, 

 * trichocyle. B, monostromatic frond seen from above; l>elo\v a trichocyte, numerous 

 fusions. C, marginal part of frond seen from above; two trichocytes are visible, one 

 with hair- D. vertical section, not median, tlirough a sporangial conceplacle; only un- 

 dividedsporangia present. E, vertical section through emptied sporangial conceptacle. 350 : 1. 



