572 Mr. Henderson on the Reproductive Organs o/'Equisetum. 



membranous bag", flattened on two sides, and reticulated in a peculiar man- 

 ner; six or more tliecœ surround the pedicel of the peltate scale to which 

 they are attached, the approximating sides being flattened, and the outer and 

 inner edges prominent. The theca is reticulated in the following manner: 

 three or more rows of muriform meshes placed transversely side by side run 

 along tlie inner edge (Tab. XXXIX. fig. 1.) ; the ends of these meshes are 

 separated by a zig-zag line (or what proves when highly nmgnified to be a 

 double line), and it is at one of these lines that the dehiscence of the theca 

 takes place (Tab. XXXIX. fig. 14. a.). The meshes occupying the sides and 

 outer edge are of various forms, generally disposed in irregular rows or 

 divided into areolte, the meshes in each of which have a different inclination ; 

 those on the outer edge arc placed longitudinally, from whicli the bundles of 

 meshes on the sides are variously inclined in the direction of, and to meet the 

 rows on the inner tt([^6 (Tab. XXXIX. fig. 2.). In this state the theca con- 

 tinues until the spores have attained their full size, and are changing to the 

 dark green colour which they assume at maturity. 



At this time a new deposit of vegetable matter is added to the membrane of 

 the theca, in which spiral vessels are developed : a deposit of green granular 

 matter is first observed round the edges of the meshes, and afterwards di- 

 spersed of a lighter colour over the whole: the development of the spiral 

 vessels immediately follows this deposit, which seems in a great measure to 

 be absorbed in the process, as the theca afterwards partly regains its former 

 transparency. On first observing this deposit, it appeared to me to be formed 

 on the inner surface of the membrane of the theca; but after examining both 

 surfaces with a magnifying power of four hundred diameters, I foimd that they 

 presented exactly the same appeai-ance. Subsequent observations, howevei", 

 have convinced me that the meshes of the theca are composed of a double 

 membrane; that they are in fact flattened cells, the united edges of whicli 

 form the boundaries of the meshes, ami that the deposit in question, and 

 afterwards the spiral vessels, are formed in the space caused by a partial 

 separation of the two membranes. This observation is confirmed by the 

 appearance of the meshes, which at this time have more or less of a blistered 

 appearance, or are wholly inflated, but again collapse as soon as the spiral 

 vessels are formed. These vessels vary according to the form of the meshes 



