Simple Plants 



207 



Fig. 97. 

 Volvox Globator, a Colonial Form of the Volvocacece. 

 (See Fig. 49, where this same form is considered an 

 animal.) 



A, mature colony, with four daughter colonies devel- 

 oping in its interior; B, section of the edge of the colony, 

 showing three vegetative cells and a developing egg; 

 C, a packet of sperms within the parent cell and a single 

 sperm very much magnified at the side; D, an egg sur- 

 rounded by a swarm of sperms; E, an oospore with 

 heavy protective wall. (From Bergen & Davis' "Princi- 

 ples of Botany," by permission of Ginn & Co., Pub- 

 lishers.) 



ago Spallanzani fertilized 

 the eggs of various animals 

 artificially, while more re- 

 cently several workers have 

 succeeded in causing eggs to 

 begin to grow by chemical 

 means. The experiment was 

 first successfully made with 

 the eggs of sea-urchins and 

 other marine animals by a 

 zoologist, Loeb. In 1913, 

 Overton successfully accom- 

 plished the same thing with 

 the eggs of Fucus. The eggs 

 were dipped in a mixture of 

 50 cc. of sea-water plus 3 cc. 

 of a very weak solution of 

 acetic, butyric, or other fatty acid, for about a minute, or a minute and 

 a half to two minutes, and then transferred to normal sea-water. The 

 formation of the fertilization-membrane was caused in this way quite 



as in natural fertilization by the 

 sperm. It was also found that, after 

 the formation of the membrane, if 

 the eggs are placed for 30 minutes 

 in hypertonic sea-water (50 cc. of 

 normal sea-water plus 8 to 10 cc. of 

 a weak solution of sodium chloride 

 or potassium chloride), and then 

 back into normal sea-water, the 

 eggs will begin to divide and con- 

 tinue to develop into young plants. 

 The chromosome number in the cells 

 of plants formed by artificial fertili- 

 zation, although a question of very 

 great interest, is still unsolved. 



Fig. 99. Phycomycetes. 



These are the alga-like fungi without septa 

 in the mycelium, except in the sporing 

 branches, where they occur to cut off the spore- 

 bearing cells. The septa also occur in old 

 filaments. The mycelium is therefore continu- 

 ous. 



Common water mold (Saprolegnia) : A, 

 a fly from which mycelial filaments of the par- 

 asite are growing; B, tip of branch organized 

 as a sporangium; C, sporangium discharging 

 biciliate zoospores; F, oogonium with an- 

 theridium in contact, the tube having pene- 

 trated to the egg; D and E, oogonia with 

 several eggs. (A-C after Thuret; D-F after 

 De Barry.) 



Fig. 98. Growth Habit of the Bread Mold 

 (Rhizopus Nigricans.) 



Sketch showing two groups of erect hyphae 

 bearing sporangia, with rootlike clusters of 

 filaments at their bases. 



