148 Sensitive Fern 



In O. sensibilis the margin of the sterile leaf-blade is very 

 minutely and obscurely more or less serrulate in all stages of 

 development. Aside from this, the blade is at first imperfectly 

 semi-orbicular, and sometimes obscurely trilobed, with sub- 

 truncate entire base and crenate or dentate upper margin. It 

 then becomes successively reniform or reniform-orbicular, with 

 undulate or crenate upper margin, reniform-deltoid becoming 

 crenately trilobed, and deltoid trilobed with deep often squarish 

 sinus at base. As development progresses, the central lobe be- 

 comes sinuate or lobed, and at length cut into segments, which form 

 all but the basal segments of the mature leaf and which, as they 

 develop, become in their turn undulate, sinuate, or pinnatifid. 

 The two lateral lobes develop into the basal segments of the 

 mature leaf and become sinuous-pinnatifid. At this stage the 

 segments above them range upward from sinuous-pinnatifid to un- 

 dulate or entire. Development of the sterile leaf as such then 

 ceases. Further change lies in its transformation into a sporophyll. 



The veins are branched and free in the first stages of the 

 leaf -blade's development. They become anastomose before 

 a mid vein shows in any very distinct fashion. One or two 

 areolae form first in the centre of the reniform or reniform- 

 orbicular blade, and others quickly follow, forming outward 

 until the margin has the appearance of cutting the network of 

 veins. The marginal veinlets are mostly free. 



When the blade becomes trilobed the areolae through the 

 centre of each lobe are straightened in such a way as to form 

 a double row, the inner common side of the two single rows 

 that make up the double one forming the midvein. There- 

 after every well-defined lobe or segment of the blade possesses 

 more or less of a midvein, similarly formed. 



