NATURAL DEPOSITION 



TABLE XII 



DEPOSITION OF SPORES ON GROUND, FROM SIMULTANEOUS MEASUREMENTS 

 OF X AND d BY VISUAL COUNTS UNDER MICROSCOPE. 



(Gregory, Longhurst & Sreeramulu, unpublished) 



Distance from source 

 Mean 



wind- 2-5 m. S'O m. lo-om. 20-0 m. 



speed p Vg p vg p Vg p Vf 



Height of 

 liberation 



Lycopodium spores 



i-o metre 1-98 



0-83 



0-62 



0-40 



0-25 metre 1-28 



i-io 



1-09 



Mean: 



Ganoderma spores 



0-25 metre 



1-70 

 0-91 

 076 

 o-6i 

 Mean: 



o-oi 



0-02 



0-44 

 0-05 

 0-07 

 0-13 



0-12 



0-022 

 0-015 

 0-014 

 0-017 



cm. /sec. 



2-3 

 1-2 



17-6 

 6-9 



7-2 



137 

 8-16 



1-97 

 I-I3 

 0-83 

 1-31 



0-02 

 0-05 

 0-09 

 0-05 

 0-03 

 O-OI 



0-04 

 0-042 



1-5 m. 



0-006 

 0-006 

 o-oio 

 0-007 



cm./sec. 



3-6 



3-8 

 5-5 

 2-1 



4-4 

 1-5 

 4-5 

 3-64 



0-56 



0-43 

 0-61 



0-S3 



cm./sec. 



0-02 

 0-06 

 0-05 

 0-02 



0-02 

 0-02 

 0-02 

 0-029 



2-5 m. 



0-003 



0-005 



0-003 



0-006 



0-004 



3-4 

 5-1 

 2-9 

 i-o 

 2-7 

 1-7 

 1-8 

 2-8 



0-44 

 0-46 

 0-24 

 0-34 

 0-37 



0-03 



0-03 

 5-0 m. 

 0-0008 

 0-004 

 o-ooi 

 0-005 

 0-003 



cm./sec. 



1-7 



1-7 



0-14 



0-34 

 0-08 

 0-29 



0-21 



Summary 



Lycopodium 

 c. 32 \x. dia. 

 va = 1-76 cm./sec. 



Ganoderma 

 <r. 10 X 6 /x 

 vi = o-i8 cm./sec. 



Mean of all values 



P Vg 



0-057 



0-007 



4-35 



0-56 



Mean at selected distance 



Vg 



2-7 at 10 metres 



P 

 0-03 



0-004 0-37 at 5 metres 



to 5 times as great. (On theoretical grounds, Schrodter (1954, i960) 

 deduced that the 'probable final velocity' of a spore is halfxht terminal 

 velocit}'.) For a deposition theory based on sedimentation under the 

 influence of gravity, it seems reasonable to accept observed terminal 

 velocities of the particles as measuring their velocity towards the ground ; 

 but for a ground-level source, allowance will have to be made for excep- 

 tionally large deposition during the first few metres of travel. Data are 

 not sufficiently extensive to bar the use of the coefficient of deposition, 

 p, which assumes that, for a particle of given size, the deposition depends 

 on the distance travelled, rather than on the time taken to travel that 

 distance. If p turns out to be independent of wind-speed, the parameters 

 p and Vg would stand contrasted in a manner recalling the different 

 treatments of a by Schmidt and Sutton (Chapter V). 



Ground deposition conforms better to a sedimentation theory than 

 does deposition on the horizontal microscope slide in the wind-tunnel 

 recorded in Chapter VI. For comparison with ground deposition. Table 

 XIII shows wind-tunnel values, calculated in terms of p and Vg, for 

 deposition on a horizontal slide. 



79 



