1 50 Miss T. L. Prankerd. On the Irritability of the 



attached to them, if at all. This, however, was the only case in which any 

 orientation of the nuclei in A. bulbiferum was ever observed. 



The very youngest tissue — an actual meristem — never contains statoliths, 

 which is scarcely possible, since little or no sap cavity is as yet developed in 

 which they can lie loose ; but, as the young frond develops, the chloroplasts 

 about the bundle at the base become free, and this gradually extends outwards, 

 till practically the whole green part of the ground tissue is composed of 

 chloro-statenchyma (photo. 3). This well-characterised tissue (4) follows, so 

 to speak, the growth of the petiole upwards, by being freshly formed as 

 development proceeds to within a centimetre or so of the apex, and dying 

 away behind as the xylem becomes lignified, and, later still, sclerenchyma is 

 developed. Since more statenchyma is formed apically than dies away 

 towards the base of the petiole, the amount gradually increases, till it 

 probably reaches a maximum as the lower pairs of leaflets develop. It never 

 seems to be found higher than the third or fourth pair, and dies away 

 altogether before the end of the adolescent phase (fig. 7). 



TTig. 7.— Fronds of Asplenium bulbiferum increasing in age from (l)-(4). Note that (4) 

 is older morphologically than (3) though smaller. Dotted area indicates amount 

 of statenchyma. 



The statolith apparatus is very beautifully shown in the fronds of 

 Asplenium bulbiferum. The statoliths are large, bright green bodies full of 

 starch, and apparently indistinguishable from chloroplasts, except that they 

 are completely free from the protoplasm and nucleus. Nearly every cell of 



