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olive family the surface is covered with a beatuiful reticulate 

 pattern, as in the grains of privet. In the holly the surface is 

 pebbled. All possible modifications and combinations of these 

 and many other sculpturings are found in association with the 

 basic three-furrowed form of grain. 



But not all dicotyledonous pollen grains have only three 

 furrows. Some have 4, 6, 9, 12, 15 up to 30, and even sometimes 

 more. As a rule these conform in arrangement to very definite 

 geometrical patterns. For example, dahlia pollen grains always 

 have six furrows arranged according to the edges of a tetrahe- 

 dron. Those of the carpet weed {Mollugo verticillata) have 

 twelve furrows arranged according to the edges of a cube, and 

 the beautiful grains of the garden portulaca often have thirty 

 furrows arranged according to the edges of a pentagonal dodeca- 

 hedron. But this is a most exceptional kind of grain because as 

 the number of furrows increases they must shorten, and this 

 they do without losing much in width, thus becoming circular 

 and coinciding in extent with their enclosed germ pores. There 

 are whole families with pollen grains of this kind, provided with 

 round holes instead of furrows, the plantains, the mallows, the 

 four-o'clocks, most of the cucurbits, the amaranths, the cheno- 

 pods, and many others. These we call pored grains in order to 

 distinguish them from furrowed grains. These pores, of course, 

 cannot function as furrows in accommodating changes in vol- 

 ume but the germinal papillae can be protruded and withdrawn, 

 and in this way they accomplish the same end, making up in 

 numbers their loss of mechanical action. Still other pollen grains 

 have only one furrow, but these are not found among the higher 

 dicotyledons; the one-furrowed grain is the sign of the gymno- 

 sperms, the lower dicotyledons, and most monocotyledons, all, 

 in fact, except such Helobieae as the arrow-heads and water 

 plantains which appear to be badly misplaced in our plant classi- 

 fications for they show their strongest affinities with the crow- 

 foot family among the dicotyledons. Thus the grains of such 

 gymnosperms as the cycads and ginkgo are long and boat shaped 

 with one long furrow reaching from end to end. Those of the 

 dicotyledonous magnolias and peppers are almost exactly the 

 same, so also are those of the lilies and some of the arums among 

 the monocotyledons. The one-furrowed type of grain is im- 

 mensely ancient, even older than the pollen grain itself, tracing 



