Tr ue, Notes on the Pli^'siology of tlie Sporophyte etc. 41 



In tlie second experiment, an attempt was made to make 

 this clear. On- March 27, a healthy ciilture of Mnium cuspida- 

 tum was potted and packed as above described and plaeed with 

 the sporopliYtes in a horizontal position. Ilhimination from be- 

 low was secured ' by means of a mirror plaeed about 8 inches 

 below the culture which reflected Höht from the eastern sky 

 npon the horizontal sporophytes. Light was admitted through 

 an opening 1 — ^4 inelies wide and "2 inches long, made by bre- 

 aking a place in the pot opposite the sporophj'tes. Except in 

 the forenoon, when some direct sunlight was reflected upon the 

 plants, strong diffused light was siipplied. 



On March 29, the yonng sj)orophytes in many cases showed 

 a slight gradual bend in the distal half in an upward direction, 

 in a manner not markedly different from tliat seen in the pre- 

 ceding experiment. At the distal end a slight downward direc- 

 tion is noticeable. broucrht abont bv a curvature of smaller ra- 

 dius near the lower edge of the caly})tra. In a few cases, the 

 sporophytes were practically horizontal except at the distal end, 

 where a downward curve was seen. 



On April 1, no increased curvature in the setal was noticed. 

 A sharp do\\Tiward curvature at the lower edge of the calyptra, 

 however. was conspicuotis, bringing the now clearly enlarged 

 capsular rudiments into a position approaching the perpendicu- 

 lar. With but three exceptions in about thirty-five individuals, 

 the tips of the calyptrae pointed almost directly downwards, 

 therefore, against the incident light rays. 



On April 10, the capsules were found to have developed 

 normaDy and were approaching their füll size. In every case, 

 the long axis of the capsule was perpendicularly directed, and 

 stood at approximately a right angle to the axis of the seta. 

 The plants seemed to be entirely healthy. 



The experiments above described seem to make it clear that 

 in the case of Mulum^ and probably of Fuuaria also, the „nod- 

 ding" of the capsules is brought about by the stimulating ac- 

 tion of gravity, since the direction of the Illumination does not 

 interfere with the tendency of the capsules to assume the ..nod- 

 ding-" or. in the case of Mnium. the pendulous position, seen in 

 nature. The partial success of the klinostat experiments points 

 in the same direction. 



The directive influence of illumination is clearlv marked in 

 determining the plane in which the capsular rudimeiit shall fall. 

 Sometimes the ajjex of the capsule falls toward the source of 

 liüht, sometimes against it. This conclusion has been tested manv 

 times by the study of Mnliun in its usual habitat. and, with 

 veiy rare exceptions, it is possible to parallel the results seen in 

 the laboratory. Occasional exceptions may bo accounted for by 

 considering the foliage conditions and the position of the sun 

 in the heavens during the day at the time'of the year wlien 

 the sporophytes are developing. Various obstacles interfering 

 with light may thus bc lurated. 



