430 EXPLANATION OF THE FIGURES. 



PLATE XLIX. 



ISOETES LACUSTRIS. 

 FIG. 



1. Longitudinal section at right angles to the furrow of the stem of a ten- 



montlis-old plant, X 30. 

 I 6 . "Woody mass and terminal bud of the same, X 300. 



2. Transverse section of the middle of the stem of a plant about eight years 



old. The principal portion of the bark and the two side lobes are 

 omitted, x 20. 



3. Rudiment of a scale seen from the surface, x 200. 



4. The same more developed. 



5. A perfect scale, X 6. 



PLATE L. 



ISOETES LACUSTBIS. 



The terminal bud and the upper portion of the woody mass of the stem 



shewn in PL XLIX, fig. 1, x 300. 

 The same parts of a stem cut through at right angles to the indentation, 



X 250. 



PLATE LI. 



ISOETES LACUSTRIS. 



1. Longitudinal section through the furrows of the stem of a plant eight 



years old, x 30. 



2. Similar section of the lateral surface of the middle region of the woody 



mass of an older plant, together with a portion of the cambium. One 

 of the cells of the latter — separated from the uext wood-cells by three 

 cambial cells — is beginning to become liquefied, x 250. 



3. Longitudinal section of a fragment of a vascular bundle from the older 



part of the bark, x 250. 



4. Transverse section near the woody mass of a vascular bundle running to 



an older frond, x 250. 



5. Terminal bud of an eight-years-old plant seen from above, X 200. 



PLATE LII. 



ISOETES LACUSTBIS. 



I. Longitudinal section of the stem (at right angles to its furrow) of a six- 

 years-old plant, X 20. 



