crowded in a head at the bottom. When nearly mature the 

 staminate flowers break away from the plant and come to 

 the surface of the water, on which they float. In this con- 

 dition it forms a ball, but when fully mature the petals turn 

 hack, forming a skiff like arrangement, the stamens length- 

 en out and the anther cells open. Each anther contians 

 thirty eight large, more or less viscid, pollen grains. The 

 three skiff like sepals are admirably adopted to float on 

 water. Short waves or currents of wind drive them along 

 until they come against a solid object, where they remain, 

 and if it be a pistillate flower the stamens come in contact 

 with it, leaving the pollen attached to the stigmas. After 

 fertilization the threads that bear the fertile flowers coil up 

 spirally, drawing the fruit under water, to ripen. 



Lemna. Species of duckweeds are admirably adapted 

 to water pollination. The following account of pollination 

 of Lema minor is based on the observations made by 

 Trelease. Duckweeds are among the smallest of flowering 

 plants and form scums on the surface of ponds and slow 

 running streams in summer. They are very simple in their 

 structure. Each fertile found produces a single flower fron: 

 a cleft in the margin. The flower consists of a single pistil 

 and two stamens and a subtending bract. When the flower 

 expands, the pistil elongates sufficiently to expose about half 

 its length beyond the tips of the marginal fissure of the 

 frond. The stigma becomes moist by the exudation of a 

 fluid; and is now receptive. In this condition it remains 

 some days when the stamen furthest from the base of the 

 frond becomes exserted, attaining the length of the pistil 

 when it dehisces, the polleLu remaining heaped in the open 

 cells of the anther. The second stamen dehisces several 

 days later. The flowers are therefore strongly proterogyn- 



