REACTIONS OF INFUSORIA TO LIGHT AND TO GRAVITY 143 



280 ^t/it wave length. In the two species last named the chief reaction 

 observed was a sudden contraction. Epistylis bends to one side under 

 the action of the light, while Paramecium bursaria reacts in essentially 

 the same manner as to ordinary light, as described above. All died 

 quickly under the action of powerful ultra-violet light. 



The flagellate swarm spores of many algae react to light. Their 

 behavior in this reaction has been studied especially by Strasburger 

 (1878). These swarm spores (Fig. 97) usually resemble Euglena in 

 essential features, though they may differ in form, in the number of 

 flagella, and in other details. They contain chlorophyll or other color- 

 ing matter, and usually a red eye 

 spot. The action system of the 

 spores is similar to that of Euglena. 

 They swim in a spiral path, keeping 

 a certain side always toward the axis 

 of the spiral (Naegeli, 1860, p. 96). 

 On coming to an obstacle, they react FIG. 97. Examples of swarm spores, 



i ., /XT i. i % after Schenck. a, Haematococcus pluvialis; 



by turning tO One Side (Naegeh, I.C.), 6>U i othr5 xzonata; c, Botrydium granulatum, 

 With or without a previous Start gamete; d, Cladophora glomerata; e, CEdo- 



backward. It is probable that the gor 



turning in response to a stimulus is always toward the side directed 

 outward in the spiral path, as it is in Euglena, Chilomonas, and Cryp- 

 tomonas. The movements of the swarm spores, so far as known, exactly 

 resemble those of the organisms just named. It is further without 

 doubt true that the anterior end is in the swarm spores, as in other 

 infusoria, the most sensitive part of the body. The swarm spores are 

 much smaller than Euglena, so that the details of the behavior are less 

 easy to determine. 



Strasburger found that when the light is weak, all the colored swarm 

 spores l swim toward the lighted side of a drop (positive reaction). 

 When the light is strong, some swim away from the lighted side (nega- 

 tive reaction). If different parts of a drop or a vessel are unequally 

 illuminated, the swarm spores gather in the lighted region. The phe- 

 nomena are thus in general similar to those found in Euglena. There 

 are certain variations among the different swarm spores. Thus, Stras- 

 burger found that Botrydium and Cryptomonas are positive even in the 

 strongest light, while in a weak light Cryptomonas is indifferent. But 

 in most species there is, as in Euglena, an optimum. In light below 



1 Strasburger studied the swarm spores of Haematococcus lacustris, Ulothrix, Chaeto- 

 morpha, Ulva, Botrydium, Bryopsis, CEdogonium, Vaucheria, and Scytosiphon, as well 

 as the flagellate Cryptomonas (called Chilomonas by Strasburger), and the colorless 

 swarm spores of Chytridium and Saprolegnia. 



