The manner of fertilization may be briefly outlined, although the observation of this is beyond the ordinary student. With Ferns, as is the case with nearly all the Cryptogams, the fertilization takes place under water; the moisture may be the outcome of heavy rain or even dew. However that may be, as soon as the underside of the prothallus has become thoroughly wetted the antheridia open, and certain little bodies called spermatozoids are allowed to escape. These are exceedingly active, and are in the form of spirally coiled bodies with a number of fine threads (cilia) at one end. The same moisture which caused the antheridia to open also brings about the opening of the archegonia. Some time ago it was shown that the spermatozoids steered a decided course towards the archegonia, but the reason for this has only been comparatively recently explained. At the mouth of the archegonia there is a viscid drop which almost certainly contains chemical substances attractive to the spermatozoids. Although the nature of the substance is not exactly known, it is suggested that this may be malic acid, seeing that experiments have shown that the spermatozoids are attracted to this product when it is artificially introduced. Of course the matter is a difficult one to prove, in that the viscid drop is so minute that it is impossible to determine the nature of the substance which it contains. Malic acid has, however, been discovered to be present in the prothallus as a whole. Although there is quite a competition amongst the spermatozoids as to which shall enter the archegonium, it is likely that only one actually succeeds in entering the egg cell. As a rule, too, in the prothallus only one of the archegonia shows any further signs of development. After the fertilization is completed the first happening is the formation of a cell-wall round the ovum. Passing through various stages of growth and subdivision it finally forms the embryo of the young plant. For a while the newly-born Fern relies upon the prothallus for sustenance, but eventually starts an independent existence. The baby sends down roots into the ground and leaves up into the air, and from thenceforward its development into a mature plant will only be a matter of time.