380 



BOTANY 



PART II 



peculiar, and the two groups of the Oomycetes and the Zygomycetes 

 are distinguished according to their nature, In the Oomycetes, 

 which stand nearer to the Green Algae, oogonia and antheridia are 

 found ; the contents of the latter enter the oogonium by means of a 

 tubular outgrowth, and after fertilisation oospores are formed. In 

 Momhlei^haris alone are free spermatozoids found. The sexual 

 organs of the Zygomycetes are alike, and on conjugation a zygospore 

 is produced. They are usually multinucleate and thus are morpho- 

 logically comparable to a whole gametangium of an isogamous Alga. 



Multinucleate gametangia, oogonia, and antheridia, which fuse 

 directly with one another, without the separation and escape of the 

 individual gametes, are generally termed Coenogametes. 



Order 1. Oomycetes 



1. Only in the small family of the Monoblepharideae (^^) are free ciliated 

 spermatozoids liberated from the antheridia. In the other Oomycetes the multi- 

 nncleate contents of the antheridiuni do not divide into separate spermatozoids, 



Fig. .%5. — Monnblepharis sphaerica. End of lilameiit with tenninal ougoiiium (u) and an antlieridinm 

 {(') : 1, before the i'orination of the egg-cells and spermatozoids ; '2, s]iermatozoids (s) escaping 

 and approaching the opening of the oogonium ; 3, osp, ripe oospore, and an empty antheridiuni. 

 (After CoRNU, X 800.) 



but are directly introduced into the egg-cell by means of an outgrowth of the 

 antheridiuni. 



The species of Monohlc-pharis live in water upon decaying remains of plants. 

 Asexual reproduction is effected by means of swarm -spores, formed in large 

 numbers in sporangia. The oogonium, which is usually terminal, contains only a 

 single egg-cell (Fig. 305). The antheridia, which resemble the sporangia, liberate 

 a number of uniciliate spermatozoids. On a sperraatozoid reaching the egg-cell 

 through an ojiiening in the tip of the oogonium an oospore is formed. A spinous 

 cell wall Ibrms around the oosjjore. 



2. The Saprolegniaceae {^^), which connect on to the preceding family, live like 

 them saprophytically on the surface of decaying plants and insects and even on 



