1912-13.] BOTANICAL SOCIETY OF EDINBURGH 185 



Seedling of Thysanotus. By Professor Bayley 

 Balfour, F.R.S. (Plate VIA.) 



Goebel figures in " Organography of Plants " (Engl. Ed.), 

 p. 409, fig. 272, a seedling of an Australian plant, probably 

 an Allium, showing a peculiar outgrowth on the surface 

 of the cotyledon at the point where its middle portion 

 breaks after its suctorial function is ended. By this break 

 — which is characteristic of many inonocotylous seedlings 

 which have hypogeous germination with the cotyledon 

 acting as the first assimilating organ — the shrunken upper 

 part attached to the haustorium within the seed below the 

 soil is separated from the lower actively assimilating part. 

 The emergence from the soil of such seedlings is normally 

 marked by and brought about by the curvature of the 

 cotyledon fixed at one end to the rooted hypocotyl, at the 

 other to the haustorium in the seed, and the green visible 

 cotyledonary part of the seedling appears as a half-hoop 

 projecting from the soil, the particles of which have been 

 pushed aside by its general growth and extension. Goebel 

 suggests that the outgrowth which he figures upon the 

 surface of the cotyledon acts as a boring organ. 



The peculiarity referred to is, I find, a character of the 

 seedlings of Thysanotus — I have seen it in T. multiflorus, 

 R. Br., T. jv/nceus, R. Br. — an Australian genus with 

 outliers in the Philippine Islands and Southern China, and 

 perhaps Goebel's species belonged to this genus and not to 

 Allium. I do not find, however, that the outgrowth takes 

 any part in promoting exit of the cotyledon from the soil. 

 It is not a boring organ, and is a late formation after the 

 cotyledon is above ground. It does not develop upon all 

 seedlings i n a braird, and its length varies. Its real 

 function seems to be to act as a hydathode and allow water 

 outgo, which is otherwise denied the seedling owing to its 

 suctorial hypogeous extremity. 



EXPLANATION OF FIGURES. 



Fig. 1. Thysanotus multiflorus, R. Br. A series of seedlings showing 

 the outgrowth on the cotyledon at the point where the apical portion 

 separates. 



Fig. 2. Thysanotus junceus, R. Br. Seedlings showing stages in 

 development. 



Photographed from nature by Robert Moves Adam. 



