PTEROPSIDA 159 



large central pith region. There is a single gutter-shaped 

 strand entering the base of the stipe, but this soon breaks up 

 into numerous small bundles. 



The sporangia are truly marginal in origin and arise in 

 strictly gradate sequence within a purse-hke box, formed by 

 the two indusia (Fig. 25G). They are long-stalked and have 

 an obhque annulus (Figs. 24M and 24N) which, in some 

 species, is very nearly vertical. The typical spore output per 

 sporangium is sixty-four. 



Matoniaceae 



This is a most interesting family, containing the two genera 

 Phanerosorus, from Sarawak and New Guinea, and Matonia, 

 from Malaya, Borneo and New Guinea. In spite of its 

 rarity at the present day, the family had many fossil repre- 

 sentatives in the Triassic. So characteristic is the method of 

 branching of the frond (Fig. 25B) that there can be little 

 doubt that the fossil Matonidium is correctly placed in this 

 family. After an initial dichotomy, each half of the frond 

 undergoes a regular series of unequal catadromic dicho- 

 tomies (i.e. each takes the main growing point further from 

 the median plane). Each pinna is pinnatifid and there are 

 anastomoses in the veinlets, particularly in the neighbour- 

 hood of the sori. Phanerosorus (Fig. 25A) has a frond of 

 indefinite growth which is long and slender and bears 

 dormant buds at the tips of some of its branches. 



The stem of Matonia is creeping and hairy, and has a very 

 characteristic polycycHc stelar structure, with two co-axial 

 cylinders surrounding a central sohd stele. From these, a 

 single gutter-shaped leaf trace is formed, both cyhnders 

 playing a part in its origin. 



The sori are superficial and consist of a small number of 

 sporangia arranged in a ring round the receptacle, which 

 continues into the stalk of an umbrella-shaped indusium 

 (Fig. 25E represents a vertical section through a young 

 sorus). There is an oblique convoluted annulus round the 



