236 INFLUENCE OF CORRELATION AND EXTERNAL STIMULI 



In my cultivations the sexual organs were laid down in autumn, and 

 therefore count was not taken of all these shoots. In the following summer 

 I noticed, as I have said, an extraordinary number of shoots, which, with- 

 out producing sexual organs, had closed their growth l . The leaves in the 

 shoots grown in feeble light were much smaller than the others, and this 

 appears in the figures. 



Hofmeister has conjectured that Fissidens, another moss with dis- 

 tichously placed leaves, owes its leaf-position to the direct action of light. 

 Here however the matter is somewhat different, because the bilaterality 

 in the shoots growing in light is produced at the apex through a ' two- 

 sided ' apical cell, from which two rows of leaf-forming segments are cut 

 off, and I have never succeeded in causing radial shoots to develop in 

 Fissidens adantioides by cultivating it in feeble light 2 ; even in darkness 

 the shoots which appeared were distichous ; and I therefore conclude that 

 in Fissidens the transition from the radial to the bilateral structure has 

 now become an inherited character, and is no longer a consequence of the 

 direct influence of light. 



The sporogonium of mosses shows in some cases a dependence upon 

 light, which may be noted here, because it is connected with the behaviour 

 of dorsiventral organs, upon the disposition of which light has a definite 

 influence. 



The capsules in the sporogonia of many mosses are radial, and either 

 spherical or cylindrical in form, as, for example, in Sphagnum, Orthotrichum, 

 Grimmia, the Phascaceae ; but in others a more or less strongly marked 

 dorsiventrality appears which, as I have shown 3 , stands in evident con- 

 nexion, in many cases at least, with the scattering of the spores. This 

 dorsiventrality arises, so far as I have been able to determine, in the course 

 of development even in the cases where it is most marked, for instance, in 

 Buxbaumieae. The young sporogonium here is always radial, notwith- 

 standing Wichura's 4 statement to the contrary, and the dorsiventral 

 construction shows itself most strikingly in this that the mouth of 

 the capsule no longer falls in a straight line with the stalk, and the 

 beak of the unopened capsule is thus placed obliquely to the shaded 

 side in Buxbaumieae, Barbula subulata, and Catharinea undulata, to the 

 illuminated side in Bryum argenteum. Whether the curvature would be 

 entirely suppressed in capsules which were cultivated through the younger 

 stages in light varying in its direction is unknown, so that the whole 



1 All the shoots of Schistostega have limited growth. 



2 Hofmeister (Pflanzenzelle, p. 140) figures a plantlet of Fissidens bryoides upon which the lower- 

 most three leaves here laid down under ground are tristichous whilst the upper leaves are 

 distichous. This is a consequence of the apical cell being at first three-sided in this plant. 



3 Goebel, in Flora, Ixxx (1895), p. 459, and Ixxxii (1896), p. 480. 



1 \Yichura, Eeitr. zur Physiologic der Laubmoose, in Pringsh. Jahrb. ii. p. 193. 



