ORIGINS OF AGAMIC PATTERNS 6oi 



rangia develop (Pfeiffer, 1907). This is essentially a multiaxiate sporan- 

 gial pattern with apical region apparently dominant, as in multiaxiate 

 vegetative stages of many plants. 



All seed plants are heterosporous with reduced gametophyte genera- 

 tion, the pollen grain representing the male, and the cells of the embryo 

 sac in the ovule, or, according to some botanists, the endosperm, repre- 

 senting the female gametophyte. Among the gymnosperms pollen grains 

 may consist of several cells in a definite axiate pattern, and the question 

 arises whether this is determined by the relation of the tetraspores to 

 each other or by some other factor. Pollens of certain conifers possess 

 two wings, developing on the outer surface of each tetraspore and sym- 

 metrical to the axis of the grain indicated by the cells composing it ; that 

 their localization and the axiate pattern of the grain are determined by 

 the relation of each spore to the others in the tetrad appears probable. 



In most angiosperms the two divisions of the spore mother cell form a 

 linear series of four cells, coinciding in direction with the ovule axis, the 

 innermost of these giving rise to the embryo sac. Polarity of the ovule 

 apparently determines, in some way, the direction of the mitoses. The 

 long axis of the embryo sac and, in the gymnosperms, of the archegonia 

 developing in it also coincides with the ovule axis and apparently de- 

 velops as part of it. The ovule itself is, in certain respects, similar to a 

 bud in origin but has a symmetry pattern definitely related to the pattern 

 of the ovary. 



Motile swarm spores (zoospores) with flagella are characteristic of vari- 

 ous algae and some fungi. The macrozoospore of Ulothrix, for example, 

 is formed by division within a cell of the axiate filamentous thallus, which 

 consists of a single cell series. One end of the zoospore is somewhat pomted 

 and bears four flagella; an axiate differentiation is also present, consisting 

 of colorless cytoplasm containing a contractile vacuole at the flagellate 

 pole and chlorophyll-bearing cytoplasm elsewhere; on one side of the 

 body is a red pigment spot, the so-called "eyespot," or stigma (Fig. 186, 

 A). In short, as often noted, these zoospores resemble flagellate proto- 

 zoa. The microzoospores (gametes) are similar in pattern, but they are 

 smaller and have two flagella. 



The same questions as to origin of this axiate, asymmetric pattern 

 arise with reference to these zoospores as for the similar protozoan pat- 

 terns. Certain early figures (e.g., Dodel, 1876) show the polarities of two 

 macrospores formed within a thallus cell as parallel, oriented in the 

 same direction at right angles to the thallus axis, and with pigment spots 



