314 



LYCOPODIALES 



_ 



and this has been found in L. inundatum to go along with a more bulky 

 origin. The sporangium as seen in radial section arises as a broad swell- 

 ing, while two cells have been seen to divide periclinally, indicating at 

 least two tangential rows of archesporial cells in place of the single row 

 in L. Selago. This origin of the sporogenous tissue may still be traced in 

 the older stages (Fig. 159). It may be that this condition is not 

 actually constant in all cases, but it has certainly been observed to exist 

 in L. inundatum. 



Of the rest of the sub-genus Rhopalostachya, Z. clavatum and L. alpinum 

 have been examined, and they both show a still more massive type of 



sporangium. This is seen 

 in the mature state (Fig. 

 1 60 q, r, s: t, u, v, w), 

 where the stalk appears 

 to be short and thick : 

 moreover, it is seen that 

 the strobilus is constructed 

 in these species so as to 

 afford more complete pro- 

 tection to the sporangium 

 while young, than is the 

 case in the simpler type 

 of Z. Selago. This is 

 effected by special de- 



, r , , 



VCIOpment OI the lower 

 c i , -,-, 



parts of the sporophylls 

 (Fig. 22 D, E): in some 



cases, as in L. cernuum, the sporophyll takes a peltate form. Radial sections 

 of the young sporangium show, both in L. clavatum and in L. alpinum, 

 that from the first the form is broader still than in the types previously 

 described. At least three cells in each radial section are involved in the 

 origin of the archesporium, sometimes even more than three (Fig. 161 A, B). 

 Occasionally periclinal divisions appear in the superficial cells, by which 

 subsequent additions may be made to the archesporial tissue (Fig. 161 B, 

 cells marked x). The . tangential sections also show an advance on the 

 Selago type : for twelve is not an uncommon number of the archesporial 

 cells in one tangential row as against seven in Z. Selago, or five in 

 Z. Phlegmaria. Countings of the sporogenous cells laid bare in sections 

 of sporangia at an age approaching the tetrad-condition show that their 

 number is far in advance of those of the Selago type : this is the condition 

 to be anticipated from the bulky character of the sporangia (Fig. 161 c, D) : 

 moreover, their thicker and shorter stalks would be well fitted to transfer 

 the necessary nourishment for the larger spore-output. It may be noted 

 that in these large sporangia occasional irregular processes project 

 upwards from the base of the sporangium into its cavity, which would 



FIG. 160. 



Drawings to illustrate the form and manner of protection of the 

 sporangia in the sub-genus A' hopalostachya, of Lycopodium. k,Z,m, 

 sections of L. inundatum ', ff, r. s. of L. alpimnn ; t, u. z>, TV, of L. 



ciavatum. x 12. 



