44 



which there are developed a continuous row of veins which 

 travelling singly a short distance then fork into two, and 

 as twins eventually reach the margin, thus producing a 

 plain flat strap-like frond. Normally, at some distance 

 from the midrib, many of the pairs of veins for a distance 

 of perhaps an inch develop each of them a line of spore 

 cases or sporangia, and to protect the pair of lines thus 

 produced, these semi-transparent indusia or covers grow 

 inwards, so that at the outset the two appear as one thin 

 skin covering the space between the veins. Beneath this 

 skin the spore heaps develop, and eventually push the 

 indusia apart and aside, until finally they coalesce and 

 appear as single long sausage-shaped masses arranged in 

 rows along the back of frond on each side the midrib 

 herring-bone fashion. This is the normal structure, but in 

 the true or barren crispums the veins do not only fork once 

 but over and over again, and as the spaces between them 

 are maintained and filled with tissue as they progress 

 toward the margin, when they eventually reach that 

 margin it is clear that the length of the frond there must 

 be much greater than in the centre next the midrib where 

 the veins are undivided. Nature, therefore, meets this 

 difference by a frilling or folding, thus forming the 

 4 ' crispum" character, and at the same time greatly 

 enhancing the charm of the plant. Comprehending this, 

 it is easy to understand that when spore heaps present 

 themselves the vein pairs which bear them and have to 

 feed them are more or less exhausted of vigour, and cannot 

 therefore complete that part of the frill which they would 

 otherwise form. Hence the margin of the fertile crispum 

 is usually more or less irregular in the ratio of fertility. 

 When such spores are sown we get young plants of 

 apparently the true crispum type, but eventually as spore- 

 bearing adults they follow the parental example and cease 

 to be perfect in the eyes of the expert. C. T. D. 



(To be continued,) 



