344 Prof. A. P. W. Thomas. 



character and abundant, and appear to place the matter in a very 

 clear light, unless, indeed, we refuse to accept evidence drawn from 

 any variations. I should state here that Professor Bower has already 

 used certain variations (chiefly variations in the way of reduction) of 

 the sporophylls of Tmesipteris as evidence as to the nature of the 

 synangium. But with one partial exception he, apparently, did not 

 -observe the variations which I propose to describe here. But the 

 material available for his investigations is stated to have been of 

 limited amount, and it is clearly in the native country of Tmesipteris, 

 that the question can be investigated to the greatest advantage, for 

 there the quantity of material available is practically unlimited, and 

 the conditions under which the plants are growing can be best 

 studied. 



The variations now to be described may be roughly arranged in 

 three categories 



1. Sporophylls with repeated dichotomy and 2 or 3 synangia. 



2. Sporophylls in which the synangium is not sessile but raised up 



on a stalk or pedicel. 



3. Sporophylls in which the synangium is replaced by a leaf lobe of 



normal appearance. 



1. A common variation of the sporophyll is that one of the branches 

 forks a second time, a second synangium of normal form being carried 

 just below the second fork. That is, a single sporophyll carries two 

 synangia, and there are three flattened leaf lobes. A less common 

 variation is for both of the branches of the first dichotomy to fork 

 .again. The stalk of the leaf divides dichotomously into two branches, 

 which are rather stalk-like in character ; each of these, after reaching 

 .a certain length, forks again, the branches this time becoming flattened 

 and leaf-like in form ; the whole leaf thus terminates in four leaf-lobes 

 or leaflets, of the same character as the two leaf-lobes of the commoner 

 type of sporophyll. There is a synangium not only at the first fork, 

 but also at each of the forks of the second order. The three synangia 

 are all of normal form and character, and may be of practically equal 

 size. 



It will be remembered that sporophylls and vegetative leaves 

 commonly alternate in zones on the same shoot. Professor Bower 

 has stated that, on the whole, abnormalities in the sporophylls and 

 synangia commonly occur at the beginning or end of a fertile zone, 

 .as if the abnormal condition might be referred to less perfect con- 

 ditions of nutrition. Whilst I have found this to be true for varia- 

 tions of reduction in the leaf-lobes or synangia, it does not apply 

 ;to these cases in which the sporophyll shows a development in excess 

 of the normal. On the contrary, they occur rather towards the middle 

 of a fertile zone, often many together, and with neighbouring normal 



