90 PROCEEDINGS OF THE ACADEMY OF [1881. 



was densely cloudy, warm and moist, but the flowers of the Draha 

 expanded just as well as under the bright sun of previous days ! 

 These facts show that we cannot refer the opening of the flowers 

 either to light or sunlight alone. Mr. Meehan believed that plants 

 not onl^^ behaved differently at different times, but in different 

 countries; and as no one, not even Mr. Darwin, seems to have 

 noted the expansion of the petals of the Draba in England, it is 

 possible that under those cloudy skies, they do not expand at all. 

 So far as he had noted here, the self-fertilized flowers of the 

 closed Drabas produced seed just as well as the expanded ones, 

 which might possibly be occasionally cross-fertilized by the small 

 sand wasps, which visited the open flowers freely for pollen. 



How habits change at times, Mr. Meehan illustrated \)\ speci- 

 mens of Lamium aviplexicanle^ a common introduced weed in 

 gardens. Dr. Bromfleld, in his Flora of the Isle of Wight, 

 notices that the flowers vary in size during the season, but that 

 the earliest ones are the largest. Here it is reversed. The speci- 

 mens exhibited had already flowered from six verticels, and had 

 mature seeds in many, but the flowers had never expanded in any 

 case. Indeed, very rarely had the closed corollas been produced 

 beyond the calyx. They were essentially cleistogene. As showing 

 how unceriain were the laws influencing this condition, when usu- 

 ally about the end of April, the perfect flowers appeared, some 

 plants would have them a week or more before others alongside 

 produced any. To all appearances, external influences were the 

 same. 



As somewhat bearing on the laws of motion, the angle of diver- 

 gence, in branches was referred to. Mr. M. exhibited branches of 

 tSaJix capi^ea. Normally the branches separated from each other 

 at a very acute angle, but the fertile anient on these branches was 

 pendulous. Under no external influence, so far as we could tell, 

 an individual appears with pendulous branches. This has been 

 increased by grafting, and is known in nurseries as the Kilmarnock 

 weeping willow. But the aments have retained their normal con- 

 dition as regards the bi'anch. The catkins are erect on the pen- 

 dulous branches, while pendulous on the erect ones. Morpho- 

 logically a catkin is but a modifled — an arrested — branch, but we 

 see by this that whatever cause induced the change from the 

 normal condition of divergence, it v/as purely local, and ceased to 

 exist before it reached the arrested branch or ament. 



These facts were offered to show that in studj^ing motility in 

 the vai-ious parts of plants, it would be well to remember that ex- 

 ternal causes had but a limited influence, and that in these cases 

 a combination of circumstances often controlled the influences at- 

 tributed to one. As, therefore, the f;icts would vary with various 

 observations, —those of one observer sometimes seeming rather to 

 conflict with than to confirm another, — it was too soon to form 

 any just conclusion as to the motive cause. What was desired 



