1911-12.] BOTANICAL SOCIETY OF EDINBURGH 69 



EXPLANATION OF THE FIGURES. 



Fig. 1. Longitudinal section through an inflorescence of Ambrosia 

 tripartita. V, growing-point of the male inflorescence ; the individual 

 capitula (with the exception of the terminal one) are placed laterally on 

 the primary axis, a, the first leaf of a male capitulum of which b is the 

 growing-point. Bl, female flower with its envelope, H. 



Fig. 2. Ambrosia tripartita. Longitudinal section through an older 

 male capititlum. V, the growing-point. 



Fig. 3. Transverse section through the peduncle of a male capitulum 

 of Ambrosia tripartita. The xylem in each of the two large conductive 

 bundles is shaded. 



Fig. 4. Capitulum of Ambrosia tripartita seen from above. Around 

 the growing-point, V, there are seen fifteen embryonal flowers in various 

 stages of development ; the involucre surrounds the whole. 



Fig. 5. Ambrosia tripartita. Transverse section through a young 

 female inflorescence-group. In the axil of a bract (Deckblatt), D, is a 

 one-flowered female inflorescence, I, with its envelope, H ; this has two 

 prophylls (Vorblatter), V, in the axils of which other inflorescences are 

 present. 



Fig. 6, I. -III. Xanthium spinosum. 



I. Longitudinal section through a young male in- 

 florescence. B, male flower with its bract, S. 

 II. Longitudinal section through a female inflor- 

 escence. Sa, Sb, the bracts (Deckblatter) of 

 two flowers, Sa v Sb v which on the side towards 

 the incurved margins of the bracts are pro- 

 ceeding to develop the floral organs. 

 III. Older inflorescence in which each female flower 

 has now the stigma developed, st. 

 IV. Xanthium strumaria. A young female inflorescence seen 

 from above. 

 Fig. 7. Ambrosia tripartita. On the left a female inflorescence, seen 

 from the outside, st, primordia of the spines which remain rudimentary. 

 H.'the envelope (clearly two-partite). Bl, flower-primordium seen 

 through the envelope (which is regarded as transparent). On the right 

 a young inflorescence seen from the outside. 

 Fig. S. Ambrosia tripartita. 



I. Fruit with its envelope, bisected longitudinally. H, en- 

 velope ; st, spines : P, pericarp : S, seed-coat (very 

 thin) ; E, embryo. 

 II. Fruit with envelope seeu from outside. 



