EQUISETUM SELAGINELLA. 365 



ing together of the spores, which brings about a gregarious 

 development of the unisexual prothallia, and hence enhances the 

 probability of fertilisation. Besides the membrane which gave 

 rise to the elaters the spores possess two other smooth membranes, 

 in close contact, and forming together, apparently, only a single 

 wall. In alcohol material the two membranes separate, and can 

 be readily seen. With a correctly-disposed spore it can be seen 

 that they are joined at one spot. At the same time the median 

 nucleus of the spore is clearly distinguishable. If we run chlor- 

 zinc iodine into such a preparation, the elaters take a dirty violet 

 colour only, however, in their inner parts, while the outer be- 

 come brownish ; the median membrane stains yellow-brown ; by it 

 this membrane becomes wrinkled. The contents of the fresh spore 

 appear green from the presence of numerous small chlorophyll bodies. 

 Reproduction of Selaginella. The Selaginelleae are hetero- 

 s porous Lycopodineae ; they possess two kinds of sporangia and 

 spores, and we will therefore turn our attention to them in order to 

 broaden our view of the Vascular Cryptogams. The Selaginelleae 

 are also known as the Ligulatae, because their leaves are provided 

 with a small ligule at the base. We will examine more carefully 

 Selaginella Martensii (Sprg.), universally distributed in plant- 

 houses. Fertile specimens are easy to recognise by the short 

 spikes which they usually develop on the ultimate branches 

 of numerous shoots. The vegetative body of the plant is spread 

 in one plane ; it bears four rows of leaves in pairs, which cross 

 one another obliquely. In each pair the upper leaf remains small, 

 the under is considerably larger. The two rows of upper leaves 

 on the dorsal surface press against the stem with their upper side. 

 The two rows of under leaves on the ventral surface are placed 

 laterally, flatly spread out, with their upper surface upwards. 

 The vegetative body of the plant is therefore bilateral and dorsi- 

 ventral ; that is, it admits only one plane of symmetry, which 

 divides the body into a right and left half, and exhibits a ventral 

 and dorsal surface. The terminal fertile spikes, on the other 

 hand, are quadrangular, provided with four rows of symmetrically 

 arranged leaves, directed outwards. We next inform ourselves as 

 to the structure of the spike, by pulling off one leaf after the other 

 with needles under the simple microscope, beginning at the base. 

 We see an ovate, somewhat-flattened sporangium stand in the 

 axil of each leaf. Even in this operation we shall have noticed 

 that many sporangia are larger, and show projecting bosses. If 



