OTHEE FORMS OF ALTERNATION. 187 



and represented in the latter by the dormant condition 

 of the microspore for some time after being shed.* Of all 

 the points of difference, therefore, above enumerated, the 

 only one left outstanding in this comparison is the per- 

 sistence of the ovule in situ, till the maturation of the 

 embryo, as contrasted with the early shedding of the " large 

 spore." Even the coniferous pollen-tube presents, as we have 

 seen, changes in its contents corresponding in some degree 

 with those which occur in the small spore of these species 

 of Cryptogamia. We seem warranted, therefore, in arriving 

 at the general conclusion that the spore of the higher Cryp- 

 togamia corresponds to the phanerogamic ovule, on account 

 of the strong analogies in their progress to maturation 

 analogies which the distinctive characters appear quite in- 

 adequate to overbalance.^ 



But it is to be observed that the comparison does not 

 extend to the so-called spores of mosses, any more than 

 to those of the lower Cryptogamia or thallogenous plants. 

 In fact, as has already been pointed out, there is no kind of 

 affinity between the corpuscules going under this name in 

 the two groups. As the whole process of development pre- 

 liminary to the formation of archegonia is absent in mosses, 

 the gap between them and ferns is wider so far as the 

 function of reproduction is concerned than that separating 

 the latter from the Phanerogamia. The prothallium of the 

 fern has been shown to have its homologue within the 

 ovule even of some flowering plants the Coniferse as 

 traceable through a distinct chain of intermediate forms, 

 but neither to fern-spore nor to its prothallium have we any 

 homologue whatever in the moss, where the antheridia and 

 archegonia are directly attached to the leafy axis like the 



* Sanderson, in Cyclopaedia of Anat. and Physiol., IV. (Veg. Ovum.) 

 f See the abstract before given of the points both of agreement and di- 

 versity, in the notice of the Reproduction of the Coniferse, Ch. II., 9. 



