CHAPTER III. — SPORES OF FUNGI. 1 07 



The spores of many Phycomycetes have the characteristics of autonomous motile 

 cells and are therefore named swarm-spores, or zoospores, as having motion like anima s. 

 They are always formed endogenously by simultaneous division (section XVIII), and 

 are liberated from the sporangium by the process of swelling described in section XX. 

 Their origin and their development, at least up to the period of germination, take 

 place only under water ; the species which produce them are inhabitants of the water, 

 or at least their sporangia find their way into water for the purpose of forming the 

 spores. The swarm-spores of the Fungi are usually roundish or ovoid protoplasmic 

 bodies without a firm cellulose-membrane. They generally contain one or more 

 vacuoles arranged in a definite manner which varies according to the species; a 

 nucleus has been found in recent times wherever it has been searched for and the size 

 of the subjects permitted. A flagellum or one or two slender cilia with the power of 

 lively motion spring from a definite spot in their surface as processes of the peripheral 

 layer of protoplasm, and by their means the spore shows a movement of rotation in 

 the water round its own axis and usually also a rapid movement of translation in 

 space in all directions. A third movement of undulation and amoeboid change of 

 shape alternates with the other two in most Chytridieae and in Monoblepharis. The 

 mechanism of all these movements is not better known in the present instance than it 

 is in other swarm-cells ; they commence in some species (Saprolegnia, Pythium, the 

 Chytridieae) inside the sporangium sh )i ly before the liberation of the spores, and the 

 cilia consequently are by that time already formed ; in other cases, as Achlya and 

 Cystopus, the cilia and the movements make their appearance after the spores have 

 entered the water. The motion under favourable circumstances only lasts a short time 

 in the swarm-spores of the Fungi, sometimes only one or a few minutes ; the spores 

 then come to rest, the cilia are drawn in or disappear, a delicate cellulose-membrane 

 is formed, and either germination ensues or other changes take place in special cases 

 which will be described further on. The direction of locomotion is not affected in 

 most of the cases of which we are now speaking by rays of light falling on the spores 

 on one side, but this is the case in certain Chytridieae ; the spores of Polyphagus and 

 Chytridium vorax * are phototactic, and the fact is all the more interesting, because 

 these Fungi are parasitic on swarm-cells which are also phototactic and contain 

 chlorophyll, namely Euglena and Haematococcus, and owing to the peculiarity just 

 mentioned they are in a position to follow the movements of their hosts and to over- 

 take them. 



It is not desirable to discuss the little known mechanism of the movement of 

 swarm-spores in this place, for that would necessarily involve the consideration of the 

 same phenomena in the Algae, where they are more open to observation. 



The zoospores of Fungi (Fig. 53) are usually ovoid or roundish lenticular with a 

 thick blunt margin, often pointed at the extremity which is in front when the spore 

 is in motion, and with one surface convex and the other slightly concave, so that when 

 seen in profile they have the shape of a bean. A roundish pellucid spot, a vacuole 

 in the granular protoplasm immediately beneath the surface, lies in the median line 

 of the concave side a little nearer the anterior than the posterior extremity, and a 

 long cilium springs from its anterior as well as from its posterior margin the 

 anterior cilium being directed forwards when the zoospore is in motion, the 



1 Nowakowski and Strasburger. See Strasburger, Wirkung d. Lichtes unci d. YVatrne auf 

 Schwarmsporen, Jena, 1878. 



