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do not proceed from the surface of the leaf, but that they ori- 

 ginate in primitive cells which are situated in the interior of 

 the metamorphosed leaf, and subsequently again disappear. 

 This doctrine was already shown in last year's report to be 

 well founded, and in the present one it is supported by Dr. 

 Schleiden's observations. 



2. That the carpel also, like the anther, proceeds only from 

 the metamorphosis of a leaf, and that the axile system takes 

 no part in it, but that the ovules always spring from the up- 

 per surface and from the margin of the carpel leaf. This se- 

 cond position is by no means to be considered as proved; nay, 

 we shall some pages further on be acquainted with the obser- 

 vations by which it might be refuted, and consequently several 

 explanations which M. Mohl has given of the sporangium 

 might be resolved in some other way. 



On account of the difference which the sporangium exhibits 

 in various families with respect to structure, the single fami- 

 lies must be considered separately, and M. Mohl commences 

 with the Equisetaceae. The sporidia of these plants are, on 

 account of their origin in primitive cells, and partly from their 

 composition of a double membrane, compared with the pollen 

 grains of phaenogamous plants, and even a similarity in the 

 structure of the sporangium with that of the anther is sup- 

 posed to exist. He also refutes the view according to which 

 each of the angular receptacles in Equisetum is considered to 

 arise from the cohesion of a whorl of leaves ; observations on 

 the fruit-bearing shafts of Equisetum Telmateja are also enu- 

 merated, which presented transitions from the verticillate shaft- 

 leaves, cohering into sheaths, to whorls of fructification, and 

 which left no doubt that the so-called receptacle of Equisetum, 

 covered with sporangia, does not arise from a cohesion of a 

 whorl of leaves proceeding from a branch, but from a leaf of 

 the shaft itself; that it represents as it were the connective of 

 an anther developed to an extraordinary size, and that the 

 sporangia situated on its under surface correspond to the se- 

 parate loculaments of an anther. 



In the consideration of the sporangium of ferns M. Mohl 

 first adduces the proof that the fronds of ferns must be as much 

 regarded as a true leaf, as the leaf of the Cycadece and palms; 

 and the want of buds in the axillae of the leaves of ferns is simi- 



