On Physostoma elegans, Williamson, an archaic type 
of Seed from the Palaeozoic Rocks. 
BY 
F. W. OLIVER, F.R.S. 
With Plates V, VI and VII and ten Figures in the Text. 
CONTENTS. 
PAGE 
I. Introduction 73 
II. Organization of the Seed 75 
1. General Features . . . . . 75 
2. Series of Transverse Sections ......... 79 
3. Numerical Variation 83 
III. Details of Structure 84 
1. The Integument 85 
2. The Epidermis 87 
3. The Ground-tissue of the Integument ....... 89 
4. The Pollen-chamber 90 
5. Pollination 91 
6. The Pollen-grains and Spermatozoids 93 
7. The Vascular System 95 
8. The Zone of Secretory Sacs . . . . . • . • *97 
9. The Tapetum .98 
10. The Megaspore-Membrane and the Prothallus . . . . . .100 
11. Undersized or Abortive Seeds 100 
12. Diagnosis ............. 101 
IV. General Discussion 102 
1. The Multiple Integument - 102 
2. The Nucellus .... ........ 106 
(a) The Zone of Secretory Sacs 106 
(£) The Tapetum 106 
(r) The Form of the Megaspore-cavity and Pollen-chamber . .107 
3. The Systematic Position of Physostoma 108 
V. Conclusion and Summary . . . . . . . . . .112 
VI. Explanation of Plates V, VI, and VII 113 
I. Introduction. 
At the meeting of the British Association at Bristol in 1875, the late 
Professor Williamson gave some account of a ‘ very distinct ’ petrified seed 
from the Lower Coal-Measures of Lancashire, for which he proposed the 
| Annals of Botany, Vol. XXIII. No. LXXXIX. January, 1909.] 
