ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 93 



The most striking peculiarity of Helminihostachys is the fertile 

 portion of the leaf, which is densely covered with sporangia, between 

 which are still green portions of the mesophyll. Each of these green 

 portions is the sterile apex of a branchlet. 



Muscineee. 



Structure and Development of certain Spores.* — H. Leitgeb 

 describes a number of examples of departure from the ordinary struc- 

 ture of the spores of cryptogams, viz. where the membrane is 

 composed of two distinctly differentiated coats like the cell-wall of 

 pollen-grains, mostly in the case of Hepaticse. With Strasburger he 

 retains the same terminology for the two coats, as for those of pollen- 

 grains, viz. extine and intine ; but restricts the latter term to an 

 inner layer consisting of pure cellulose. In Osmunda, Oeratopteris, 

 and Gleiclienia, for example, there is no true intine or endospore, the 

 inner layer of the spore-membrane being completely cuticularized, 

 and showing none of the reactions of cellulose. Again, in many thin- 

 walled spores which germinate immediately after maturity without 

 any period of rest, as in those of many Jungermanniacese, Junger- 

 mannia, Lophocolea, Lepidozia, Blasia, &c., there is only one membrane 

 with cuticularized outer layer, the whole of which is used up in the 

 formation of the germinating filament. This is exactly comparable 

 to certain pollen-grains, as those of Naias and OrcMs, and in a certain 

 sense also those of Allium fistulosum, where there is only one mem- 

 brane, the whole of which goes to the formation of the pollen-tube. 

 In other cases again, an inner layer of cellulose employed, in the 

 formation of the germinating filaments, is formed only immediately 

 before the period of germination. 



In many thick-walled spores of HepaticsB, the wall always con- 

 sists of more than two distinctly differentiated layers ; the exospore, 

 extine, or sporoderm being composed of two separable layers, similar 

 to the well-known case of Equisetum. 



One type of this structure is furnished by Preissia, Buvallia, 

 Heboulia, Fimbriaria, and PlagiocJiasma. The intine, which turns 

 blue and swells strongly with chloriodide of zinc, is inclosed in a 

 cuticularized layer, which is entirely structureless, and may be 

 termed the extine. This is again inclosed in a third layer with 

 folded protuberances, and elevated like a bladder on one side. But 

 slightly different are the spores of Grimmaldia and BoscJiia. 



Corsinia resembles these genera in the structure of the intine and 

 extine, but that of the outermost layer is very different. It is of 

 uniform thickness (as much as 20 fx), and is composed on the dorsal 

 side of polygonal (usually hexagonal) plates, while on the ventral 

 side it is a continuous perfectly smooth shell. Where the dorsal 

 and ventral sides meet, is a projecting seam. 



In SpJicerocarpus, the spores remain united into tetrahedra ; but 

 this is not, as in Lycopodium, the result of a simple attachment of the 

 adjacent walls ; they are inclosed in a common membrane which is 



* Ber. Deutsch. Bot. Gesell., i. (1883) pp. 246-56. 



