EXPLANATIONS OF THE PLATES. 595 



of the development of the spore of the fungi, if the steps a, b y c, d y e y f are com- 

 pared, whilst g,g represent the cicatrices of pollen-spores : see the text, $ 84>. 



Fig. 9. Borrera ciliaris. Development of the spore, 88. a. A full-grown 

 spore-case filled with a thickish cytoblastema, in which can be discerned individual 

 cell-nuclei. The wall of the spore-case is gelatinous and very thick ; b is a much 

 younger spore-case ; c y the fibres of which the disc of the sporocarp is formed 

 ( 88, fig. 127.); d, a spore-case with almost perfectly-formed spores. If the 

 spore-cases at the various stages of their growth are separated from the sporo- 

 carps, and their contents accurately examined, they will be found to constitute a 

 series such as are represented from e (a free cytoblast) to s (a perfectly ripe 

 spore). In fis seen the formation of the primary simple spore, in g, k, i the 

 gradual destruction of the nucleus, in k, /, m the appearance of two cytoblasts, 

 around which, from n q y two cells organise, till at last, in r and s, the primary 

 spore is dissolved, and the double spore appears perfectly completed. 



Fig. 10. Sphagnum cymba:folium (A. E.) and Polytrichum commune (-F-). 

 Formation of the Antheridia ($ 102. Z).) A. Youngest condition of Antheridia 

 ever observed by me. B. Perfectly-developed organ, consisting of a cellular 

 peduncle and an oval sac, which are formed out of a layer of cells and a large 

 central cell, as is shown in the section, fig. D., which was accidentally made. 

 C. The central cell isolated and burst by gentle pressure, with its contents, con- 

 sisting of gum, sugar (?), albumen, and half-solid, nitrogenous (?) granules. E. 

 The contents of the central cell at a later period, consisting of free cytoblasts 

 and very delicate flat cells, in which the nucleus is yet recognised, and which 

 gradually elongates and appears to be converted into the moving spiral fibres. 

 F. Various forms of moveable spiral fibres (so-called spermatozoa). The so-called 

 head is evidently unessential, as its form is constantly changing. 



PLATE III. 



Figs. 1 11. Pisum sativum. History of Development of Leaf. 



Fig. 1. Germinating plant, a, Root ; b y cotyledons ; c,d y e,f, first to fourth 

 leaf. 



Fig. 2. A cotyledon seen from the inner side. Where the sheathing petiole 

 passes into the disc of the leaf, are seen two little processes, which are the first 

 indications of stipules, and formed by the upward pressure of the bud during its 

 development. 



Fig. 3. Second leaf seen from the back, small lanceolate, with two lanceolate 

 (so-called adherent) stipules. 



Fig. 4. Second leaf seen from the back, small lanceolate with two large 

 stipules. 



Fig. 5. Third leaf, front view, with two leaflets and two stipules. 



Fig. 6. Terminal bud. a, Leaf spread out ; b, point of the same ; c, termin- 

 ation of the axis ; d y plane on which the leaf originates. 



Fig. 7. Third leaf separated from the foregoing terminal bud. a. Stipules ; 

 b, point of the leaf; c, leaflets. 



Fig. 8. Fourth leaf of the same bud. a y b, c. The same as in the last figure. 



Figs. 9 1 1. Three terminal buds in various ages of the leaves, seen from above. 

 The leaves of figs. 11 of, 10 c y 9d, 10 c y 1 1 c, 9 c, exhibit a perfect series of stages 

 of development, which may include also those opposite figs, at We. and 1 1 d. at the 

 youngest period of growth. It results from this, with direct evidence, that the 

 stipules are the last parts of the leaf to appear, as they originate in a part of the 

 stem where no other parts of the leaf are ever found. It is also impossible that 

 the stipules should alternate at any time with the first pair of leaflets. 



Figs. 12 20. Canna exigua. Development of the Flower. 



Fig. 12. Youngest condition. The calyx (a, a', a"} and the external circle of 

 the corolla (b y b f , b") are as yet alone present, but long before this the cavity of 



Q Q 2 



