788 PROFESSOR A. ANSTRUTHER LAWSON ON 



regular. It may bifurcate in a dichotomous fashion or a branch may grow out at 

 right angles to the main axis, as shown in figs. 2 and 3. 



One of the most striking features of the prothallus is the presence of numerous 

 long rhizoids. These rhizoids are borne on all sides. They are of great length, 

 frequently attaining a length half that of the prothallus itself, and in growing out 

 from the surface take on very curious twists and spiral shapes, as indicated in figs. 

 1, 2, and 3. All of the specimens were found at least half an inch below the surface. 

 From this as well as for other reasons I conclude that the prothallus is strictly 

 subterranean. No evidence whatever was found of their appearing on the surface of 

 the substratum in which they were growing. It was with the greatest difficulty 

 that they were isolated from the particles of soil and sand which clung very closely 

 to the rhizoids. The tissue of the prothallus itself is extremely soft and fragile, and 

 more than one specimen was destroyed in my attempts to remove the particles of 

 sand and soil by means of a soft camel's-hair brush. It was only with the greatest 

 of care that such particles could be removed. Such removal was quite necessary in 

 order to observe accurately the surface cells of the prothallus and the reproductive 

 organs. The least particle of grit left on the surface made it impossible for micro- 

 tome sections. 



The colour of the prothalli is a feature to be noted. They are of a light brown, 

 very similar to the colour of the hairs and soil clinging to the surface of the trunks 

 of the tree-ferns, or in the soil in which they .are growing. This close harmony in 

 the colour of the prothallial tissue and the substratum in which they grow has no 

 doubt been one of the reasons why these structures have not before been discovered. 

 As a matter of fact, the specimens that I have found were first recognised while 

 examining the substratum with a binocular microscope. With the naked eye it is 

 difficult to distinguish a prothallus from a fragment of a young rhizome. The first 

 specimen found was really thought to be a portion of a rhizome, but later study and 

 the discovery of additional specimens by the same methods has proved this first 

 specimen to be an undoubted prothallus. 



As stated above, the colour is characteristic and constantly brown, and in none 

 of the specimens found was there any trace whatever of the pigment chlorophyll. 

 In this connection it is of importance to note that the prothalli studied consisted of 

 living tissue. This was proved to my satisfaction by the appearance of the living 

 cytoplasm and nuclei in the cells. Had the prothalli been dead when found, the 

 absence of chlorophyll might be accounted for on basis of decay and disintegration 

 of the protoplasm. The cells, however, were living, and I am inclined to believe that 

 chlorophyll is normally absent, and that these prothalli do not depend upon photo- 

 synthesis for their initial food-supply. This absence of chlorophyll is quite in 

 harmony with their subterranean habitat. 



When we consider the saprophytic nature of Lycopodium, Botrychium, and other 

 subterranean Pteridophyte prothalli, it is not surprising to find this same habit in 



