142 INTERNATIONAL CONGRESS OF VITICULTURE 



"It has been stated by some authors that the swarmspores are constantly 

 changing their shape when swimming about. It appears to the writer, how- 

 ever, that there is no actual change, the apparent change being due to the 

 rolling motion of the spores as they swim. This, combined with their 

 peculiar shape, produces the illusion." 



"The size of the swarmspores varies, being 6 to 7 by 7.5 to 9/*. The 

 flagella are from 27 to 33/i in length." 



"After swimming about for approximately one-half hour the swarmspores 

 gradually come to rest, round up and surround themselves with a thin 

 membrane." It has been previously pointed out that they may continue 

 active for a much longer time if the temperature is low. "They apparently 

 do not immediately 'drop' their flagella but, rather, absorb them, because, 

 after becoming globose, they continue to whirl and move back and forth 

 until they gradually come to rest. They would probably stop abruptly if 

 the flagella were immediately dropped. Staining which has clearly revealed 

 the flagella on the motile forms, has failed to reveal them lying free among 

 the quiescent forms in the same preparation." 



"The spores remain globose for fifteen minutes, more or less, and then 

 there appears a slight protuberence from one side. This is the germ-tube. 

 It elongates and the contents of the spore follow. This continues until the 

 contents have passed out into the tube, leaving the thin wall. After the 

 tube reaches a certain length there may be produced an appressorium from 

 which another tube arises later." In certain cases it has been observed that 

 the swarmspores do not germinate but become very much more granular 

 and finally seem to disintegrate entirely. At times this occurs almost to the 

 exclusion of the germination. 



"The germ-tube grows parallel to the surface of the leaf until a stomate 

 is encountered when it turns sharply downward, passing through the open- 

 ing into the leaf but never penetrates the epidermis directly. In order to 

 pass through the stomatal opening the germ-tube becomes very greatly 

 attenuated, being .4 to .8//, in diameter but swells immediately after passing 

 into the sub-stomatal cavity forming a structure which, at times, closely 

 resembles the germinating spore (PI. I, figs. 1 to 11). 



Pole-Evans (1907) has termed a similar structure in the case of the 

 rusts, a sub-stomatal vesicle. Istvanffi interprets it in this case, however, as 

 a secondary spore. Its assumed function may best be stated in his own 

 words. "The physiological role of the secondary spore is in our estimation 

 to assure the ulterior development of the germinating zoospores, for this 

 reason all the protoplasm of the zoospore passes into the secondary spore 

 which is well protected against all unfavorable exterior factors in the moist 

 sub-stomatal cavity." This explanation of the peculiar behavior of the germ- 

 tube seems very reasonable. The term "secondary spore" is, in the writer's 

 opinion, also very apt because in many instances, in fact in practically all 

 instances, it closely resembles the spore from which it arose. It germinates 

 by means of one or more slender hyphae (PI. I, figs. 2, 4, and 11), and 

 according to the writer's observations does not produce haustoria hence 

 does not serve to absorb food except that which may possibly be present in 

 the intercellular spaces. 



There are many variations in the size and form of the secondary spores. 

 In some cases, especially in the leaves of susceptible varieties, the entire 



