MetapJiyta Selaginella. 1 3 1 



moreover, has its parts arranged so that the primary root 

 points towards the mouth of the canal, and consequently is 

 able to reach the exterior with the minimum amount of 

 difficulty, whilst one primary leaf is developed by which the 

 embryo first obtains nourishment from the atmosphere on 

 its own account. These various peculiarities will be referred 

 to later on when we come to examine the much more 

 complicated embryology of the ' flowering plant.' 



There is a large variety of ferns, most of which are 

 familiar objects to many whose tastes do not lie exactly in 

 the way of morphological and etiological research. Osmund.i, 

 Polypodium, Asplenium, Scolopendrium, Aspidium, Adiantum, 

 are all familiar names to fern collectors. There are, how- 

 ever, verv many extremely interesting allied forms, amongst 

 which botanists must look for the explanation of the mode 

 of origin of those anomalies in structure and development 

 which yet await elucidation. Such forms as Marsilea, Sal- 

 7'ifiia,Afara//ia,Sind Ophioglossum, especially claim attention, 

 but the extent of the present volume forbids more than the 

 mention of their names. 



SECTION II. LIGULATVE SELAGINELLA. 



In the preceding section we saw that the fern illustrated 

 very well the principle of alternation of generations in 

 plant life-history, i.e. the intervention of an asexual plant 

 between two sexual thalli. In the moss we found that this 

 alternation of generations was present, but masked by the 

 parasitism of the asexual on the sexual plant. In the type 

 we have now to consider we shall find that the converse 

 holds good, namely, that the sexual thallus is parasitic, for a 

 considerable time at least, on the asexual plant. Selagi- 

 nella, the plant commonly known as a Lycopodium or club- 

 moss in hot-houses, i.e. the asexual plant, produces spores, 

 which in their turn produce sexual thalli, only the sexual 

 thalli never leave their parent asexual plant, and, indeed, 



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