136 



MOSSES AND FERNS 



CHAP. 



the surrounding tissue of the gametophyte. This sheath keeps 

 pace with the growth of the sporophyte for a long time, but 

 finally the sporogonium grows more rapidly and projects far 

 beyond it, and this remains as a tube surrounding its base. 

 The growth of the sporogonium continues as long as the 

 gametophyte remains alive, and in A. fiisiformis is often 6 

 centimetres or more in length, and reaches nearly this length 

 before the first spores are ripe and the capsule opens. This it 

 does by splitting at the top into two equal valves between 

 which the dried-up columella protrudes. The split deepens as 

 the younger spores ripen, and may finally extend nearly to the 

 base. It is quite possible, although this point was not 



investigated, that the line of 

 dehiscence corresponds to the 

 primary vertical wall in the em- 

 bryo, as is the case in the 

 Jungermanniacese. 



The germination of the 

 spores ^ has hitherto been ob- 

 served only in A. Icevis. A study 

 of the germination in A. fusi- 

 fonnis shows a general corre- 

 spondence with the results of 

 other observers, but certain points 

 were brought out that do not 



Fig. 65.— a, young ; B, fully developed stoma SCCm tO liaVC bcCU obscrVCd in 

 from the epidermis of the sporogonium of ,4. ^ , . ,-^, ~ . ^ . 



i<evis, X250. A. IcBvts. ihe spores 01 A. fusi- 



forinis are protected by a perfectly 

 opaque black exospore, which is covered with small spines or 

 tubercles. These spores will not germinate readily when fresh, 

 but after resting for a few months grow freely. As in other 

 similar spores, the exospore is ruptured along the three ridges 

 upon the ventral side {i.e. that with which it was in contact with 

 the other spores of the tetrad), and through this cleft the endo- 

 spore protrudes as a papilla which sometimes grows into a very 

 long germ tube, or more commonly divides before it reaches a 

 great length. Into this tube passes the single chromatophore 

 which, during the early period of germination, has resumed its 

 green colour, and with it the oil drops and other contents of 

 the spore. A good deal of variation was observed here in the 



^ Hofmeister (l) ; Gronland (i) ; Leitgeb (7), vol. v. p. 29. 



