LIFE HISTORY OF A FERN 



II 



always possess some form of annulus. As the sporangia 

 mature the spore-case itself becomes differentiated into 

 two distinct kinds of tissue, namely, vegetative tissue on 

 the outside, forming the wall and reproductive tissue within, 

 from which the spores are developed. 



7. Niunber of Spores.^The number of spores pro- 

 duced by a vigorous fern is a great revelation to one who 

 has never given such matters . careful thought. Pro- 



FiG. 13.— Types of fern sporangia. A, Loxsoma CunninghaiAl; E, 

 Gleichenia circinata; C, Todea barbara; D, Thyrsopteris elegans; E, Matan& 

 peclinala; F, Lygodmm japonicum. (Redrawn from various sourd^.) 



' „■!'-:■*'■ ^ 

 fessor Bower, of Glasgow, has called attention to thjs,f act 

 in" the following words : , -' '"' 



"A rough. estimate may be made of the numerical output of spores ffom 

 a large plant of the Shield fern, as follows: In each sporangium 48' 

 spores may be formed; a sorus will consist of fully 100 sporangia, usually 

 more; 20 is a moderate estimate of the sori on an average pinna; there may 

 be fuUy 50 fertile pinnae on one well-developed leaf, and a strong plant 

 would bear 10 fertile leives. 48 X ico X 20 X 3° X 10 = 48,000,000. 

 The output of spores on a strong plant in the single season will thus, on a 

 moderate estimate, approach the enormous number of fifty millions." 



8. Types of Sporophylls — In many ferns the leaves 

 serve both vegetative and reproductive functions in about 



' Bower gives this number as the characteristic output for the species 

 Aspidium Filix-mas. In other species the number may be 64. 



