Page:Proceedings of the Royal Society of London Vol 69.djvu/304

288 theridial cavity is elongated at right angles to the neighbouring surface. The cover cells form a single layer. The sexual organs would seem to resemble those of L. cernuum more closely than those of other species of Lycopodium. There are no multicellular paraphyses amongst the sexual organs as in L. Selago and L. phleg- maria, but on some parts of the crown the surface cells are slightly papillose.

The thickness of the tissues renders it impossible to follow the details of the early development of the embryo, except in microtome sections. But it seems clear from the stages which have so far been examined, that the development at first is much like that of the embryo in L. cernuum. ^The embryo grows obliquely downwards and outwards, the part near the archegonial venter is the foot, at the opposite end are formed the stem-apex and leaf. The first part of the embryo to appear outside the prothallium is the tip of the leaf ; it breaks out at a point on the side of the thicker part of the pro- thallium, below the crown ; a fissure extends thence down the side of the prothallium, and the embryo appears as a short, cylindrical body, bluntly pointed at both ends, placed vertically, and still connected with the prothallium by the foot, which now has a lateral position. The ends of the embryo grow downwards and upwards respectively, and at a later stage what is really the apex of the stem appears inside the lower part of the embryo that is, the embryo immediately on escaping from the prothallium forms a protocorm, apparently in the same manner that the adult plant forms its annual tuber. The pedicel of the tuber elongates downwards until the latter is placed at a safe depth, about 3 mm., in the soil. In the meantime the leaf grows up and attains a height of 2 to 5 mm. above the ground. I have not hitherto seen any formation of root during the first year of growth, the sporophyte seemingly depending largely for its supply of moisture upon the prothallium, which sometimes retains its vitality even after its crown becomes injured by drought. But sometimes, at any rate, rhizoids may be developed on the pedicel and protocorm. The leaf becomes green even before it escapes from the prothallium, and as soon as it reaches a little above the soil stomata are formed, and air passes into the intercellular spaces, whilst a slender strand of tracheids appears in the centre. The first protophyll has in fact exactly the structure of a small leaf as produced in later years. The further development of the sporophyte appears to be slow. By care- fully dissecting out the plants in the soil one can find the remains of tubers and roots produced in former years. In many cases the plant comes up a second and a third year with only a single leaf. j

It should be mentioned here that Crie has stated that he sowed the spores of Phylloglossum and obtained a colourless prothallium like that of Ophioglossum. But his statements have not been accepted,