Organography of plants, especially of the archegoniatae and spermaphyta . 1 that like variation occurs also in Anthoceros (Fig. 94) whilstin Dendroceros a cell-body arises at once. We shall find that the sameproblem, and in quite the same form, arises for consideration in theformation of the prothalli of ferns. 2. MARCHANTIEAE AND We may refer to the case of Preissia commutata (Fig. 95)which has been already mentioned 2. The individual differences in thegermination of the Marchantieae, when compared with the other thalloseHepaticae, depend upon the fact that the young plants
Organography of plants, especially of the archegoniatae and spermaphyta . 1 that like variation occurs also in Anthoceros (Fig. 94) whilstin Dendroceros a cell-body arises at once. We shall find that the sameproblem, and in quite the same form, arises for consideration in theformation of the prothalli of ferns. 2. MARCHANTIEAE AND We may refer to the case of Preissia commutata (Fig. 95)which has been already mentioned 2. The individual differences in thegermination of the Marchantieae, when compared with the other thalloseHepaticae, depend upon the fact that the young plants are not developedin the same direction as is their pro-embryo. The pro-embryo is positivelyheliotropic. It forms atits end a flattened cell- mass, the germ-disk, atright angles to the direc-tion of the light-rays, andout of one quadrant ofthis the new plant pro-ceeds. This plant makeswith the germ-tube pri-marily a right angle, butthe sharpness with whichthis is marked varies indifferent forms . By thewithering of the germ-tube the plant reachesthe soil and the whole. Fig. 95. Preissia commutata. Half-diagrammatic representation ofthe germination of spores. In figures 1 and 5 the spore is shown below.], the g;erm-tube is very short aiid bears at its end a cell-mass, the germ-disk, the end-cell of which is divided by quadrant-walls. 2, in one quadrantof the germ-disk seen from above the apical cell, s, of the young plant hasbeen formed, 1, i the first segment-wall; 2, 2 the second segment-wall. :>,germ-disk seen from above showing apical cell, j, of the germ-plant formedfrom one of the halves resulting from division by the first segment-wall 1, , the direction of growth of the young plant forms an angle of 90=* withthat of the pro-embryo ; seen in optical longitudinal section. 5. the apicalcell of the young plant has grown out into a germ-tube. See also Part I,Fig. 118. arrangement is directed to bringing the plant into the light should the sporesgerminate lying between s
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