112 



WISCONSIi^ ACADEMY SCIEKCES, AETS, AlsD LETTERS, 



colors are found, upon close examination, to be owing to other 

 minute one-celled plants, called Protococcus. 

 They are little sacks or cells, containing particles of a brilliant 

 carmine red, or a beautiful green color. Each particle 

 within the cell is destined to become a new plant, and then 

 again to give origin to others. 

 The analogy between these full-grown plants of an exceedingly 

 low grade and the pollen-grains of a rose, standing at or near 

 the head of the plant-kingdom, is at once apparent. They' 

 contain particles (fovilla) destined to the same office of re- 

 production. One wood-cut serves to represent both. 



The Botrydium (Fig. 3) may be deemed a plant only a little 

 higher than the Protococcus, It consists like that 

 of a single cell; but this cell sends down a tube- 

 which is often branched, extending off in various 

 directions, Yery much like roots in search of vege- 

 table food. The cell proper is filled as usual with 

 ,f)) the reproductive particles, and some of the branches 

 become enlarged, (as shown in the figure,) develop, 

 other particles, and soon separate to form new plants of the same- 

 kind. 



In this, and in many similar full-grown plants of the lower orders, 

 there is a very striking correspondence with the pollen-grains after 

 they have fallen upon the stigma, and developed the pollen- f^ 

 tubes, (Fig, 4.) In both cases we have a cell with a tube ex- 

 tending downwards from one side, with the vegetable par- 

 ticles and fovilla; and in both, these minute bodies are sup- 

 posed to pass down the tube to perform their office of origi- 

 nating a new plant. 



Here, again, the full grown Botrydium corresponds with 

 the embryonic pollen-tubes of higher plants, and we have a 

 third proof of the existence of the law. 



■■i Fungi are plants of a higher grade than the Alg^, the Protococcus ^ 

 and Botrydium, Instead of a single cell, they consist of an aggre- 

 gation of cells ; and they produce a number of little cases .or sacks,, 

 filled with grains called spores. 



Fig. 1. Protococcus. 

 Fig. 3. Botrj'dium. 



Fig. 2. Pollen-grain. 

 Fig. 4. Pollen-tube. 



