SPORES AND THALLIDIA. 



23 



which has not been in any way a result of fertilization. These aggregates of cells 

 are, in a manner, structures intermediate between the unicellular spores and the 

 buds, differentiated into axis and leaves, which occur in vascular plants. They 

 are portions of the thallus which produced them, and are either very like it or 

 assume the same form as soon as their further development is complete. Hence 

 the most appropriate name for these bodies is that of thallidia (öaxxös = young 

 shoot; ei8os = Sü likeness). They are also known as gemmcß. Thallidia are some- 



Fig. 196.— Thallidia of Musciiieae. 



1 Marchaniia polymorpha with cups containing thallidia or gemnise. ^ 2 Longitudinal section of thallidia! or gemmiferous cup. 

 3 A single thallidium. •• Tetrwphis pellucida. 5 a stem of Tetraphis bearing a cup containing thallidia. 6 longitudinal 

 section of a thallidial cup. ', s Isolated tliallidia of Tetraphis. 9 A stem of Leucodon sciuroides with brood-bodies, i« A 

 brood-body set free from the stem, n Development of a brood-body from the rhizoids of a leaflet torn from Campylopus 

 fragilix. 12, 13, u Development of thallidia at the apex of a leaf of Syrrhopodon acaber. is Aulacomnion androgynum. 

 16 A stem of the same bearing thallidia. 17, is Single isolated thallidia. 1 natural size ; ■», is x 2 ; 2, 12, 13 x from 8 to 15 ; 

 5, «, 9, 10, 14 X from 20 to 40 ; 3, 7, 8^ 17^ is x 120. 



times in the form of rows of cells, as, for example, those developed on the leaflets 

 of the Moss Syrrhopodon scaber (see figs. 196 ^^'^^' ^^); sometimes they are nets, as in 

 the Water-Net (Hydrodictyon, see figs. 197 ^' *• ^). In the Moss Tetraphis pellucida 

 (see figs. 196 4.5,6,7,8^ they occur as plates of cells, and in other cases they assume the 

 form of globular or ellipsoidal lumps of tissue, as, for instance, in the M.O&S Aulacom- 

 nion androgynum (see fig. 196iS'i'^'i'''i8). Sometimes the number of cells associated 



