PRINCIPAL GROUPS OF PLANTS. 5 



in water or in moist places, these cells are provided with short 

 thread-like appendages known as cilia, which enable them to 

 move about in the water. They are known as ZOOSPORES or swarm 

 spores (Fig. 5, B, C), and each individual zoospore is able to 

 produce a new plant. 



The number of zoospores formed in a sporangium is usually 

 2 to 8, as in Ulothrix, but the number may be larger. The method 

 of cell formation which gives rise to zoospores is sometimes 

 spoken of as INTERNAL DIVISION from the fact that they arise 

 within the old cell and retain no relation to the old wall as is the 

 case in cell fission. The zoospores are at first naked protoplasts, 

 but later, on coming to rest, may form a wall. Sexual spores, on 

 the other hand, are formed by the union of two cells known as 

 GAMETES. When the gametes are similar the resulting spore is 

 known as a ZYGOSPORE or zygote (Fig. 5, E, F, G). When the 

 gametes are unlike, the spore produced by their union is known 

 as an OOSPORE. In the latter case one of the gametes is larger 

 than the other, is less active, and is spoken of as the female 

 gamete, oosphere, or egg (Figs. 12, 21). The other more active 

 cell is known as the male gamete, antherozoid or sperm (Fig. 

 51, ///). The cell giving rise to the oosphere is known as the 

 oogonium (Figs. 12, 21), while the one in which the anthero- 

 zoid or sperm originates is called the antheridium (Figs. 12, '21, 



22, 51). 



PLANT GROUPS. 



Until a comparatively recent time, botanists divided the plant 

 kingdom into two large groups, as follows : 



The flowering plants, or Phanerogams, meaning " reproductive 

 process evident," so applied because the reproduction of the plant 

 was readily seen to develop in the flower through the agency of 

 the pistil and stamens. 



The non-flowering plants, or Cryptogams, meaning " repro- 

 ductive process concealed," so applied to the lower plants like 

 the ferns, mosses, sea-weeds, etc., because in these plants the 

 method of reproduction was not known. 



Now, however, after a considerable amount of study, it has 

 been learned that a great many of the lower plants have repro- 



