TRANSACTIONS OF SECTION K. 859 



2. The new Botanical Laboratory at Cambridge. 

 % Professor H. Marshall Ward, F.R.S. 



3. The Seed of Lyginodendron. 

 By Dr. D. H. Scott, F.R.S., and Professor F. W. Oliver. 



4. Fruit-dispersal in Adenostemma viscosum, Forsf. 

 By R. H. Yapp, 31. A. 



Adenostemma viscosum is a Composite which is widely distributed in the 

 warmer regions of the globe. The pappus in this plant is represented by several 

 (usually three) stalked glands, by means of the secretion of which the ripe fruits 

 are firmly attached to passing animals, and so dispersed. 



During the time of flowering the gland-stalks are erect, and lie against the 

 corollas of the florets. When the fruits are ripe, the corollas fall oft' en masse, 

 being tied together by numerous filamentous hairs which clothe their upper ex- 

 tremities. The corollas and styles, as well as the ripe fruits, are cut ofi" by special 

 absciss mechanisms, which consist partly of fragile thin-walled parenchyma, and 

 partly of thick-walled mechanical tissue. The involucral leaves are at first erect, 

 then become spreading, and finally reflexed, while the receptacle becomes 

 markedly convex. Thus the achenes, when ripe, are freely exposed. Tn the 

 meantime the glands (which are composed of numerous capitate glandular haira, 

 thickly covering the upper parts of the pappus-setae) have excreted a copious 

 viscid fluid,^ which causes them at this stage to bear a marked resemblance to the 

 tentacles of a Drosera leaf. The pappus-setse also bend down till they assume a 

 nearly horizontal position, thus affording the three glands a more extended base by 

 which to adhere. This movement is effected by a group of motor-cells which form 

 a pulvinus at the base of the stalk of each gland. 



Certain other Composites have also been examined, and it is found that the 

 hygroscopic movements of the pappus is in some other cases (e.gr. species of 

 Tara.vacum, Tragopogon, Lactuca, Hypochoeris, &c.) due to similar motor-cells, 

 forming a continuous pulvinus situated just below the pappus. 



5. On Honioeomorphy among Fossil Plants, 

 By E. A. Newell Arber, M.A. 



It is fully recognised that among recent plants species of different descent may 

 possess many closely identical characters as the result of adaptation to particular 

 conditions of the environment. Such xerophilous plants as Cactus, Euphorbia, 

 and Stapelia are instances among many which might be quoted. 



It is interesting to find that there is some reason to believe that similar instances 

 of parallelism of development may be found among fossil plants. Attention has 

 been called to this subject by recent progress in the study of fossil invertebrates. 

 It has been pointed out by Mr. S. S. Buckman in regard to the Jurassic brachio- 

 pods, and by Messrs. Nicholson and Marr with reference to the graptolites, that 

 species sprung from different stocks commonly exhibit ' the phenomenon of 

 similarity in general with dissimilarity in detail,' and such have been termed by 

 Mr. Buckman homceomorphs. 



' The character of this secretion has not yet been examined, as only alcohol 

 material has hitherto been available. Specimens of this plant are, however, now 

 growing at the Cambridge Botanic Garden, from seed kindly sent by Mr. Macmillan 

 of the Royal Botanic Gardens, Peradeniya, Ceylon ; and it is hoped to decide this 

 point in due course from fresh material obtained from this source. 



