It is possible that the immediate response to tapping is partly due to a reduction in the viscosity of the latex, which is thus enabled to flow more freely. When part of the latex is removed from the vessels by tapping, the internal pressure of the latter is reduced and the remaining latex is diluted by the entrance of sap from the surrounding cells. The pressure in the surrounding cells may also be increased owing to the irritation consequent upon wounding. It is a fact that the proportion of caoutchouc in the latex often falls off rapidly during the first few tappings. The important point to be observed, however, is that the yield shows no diminution for a considerable period in spite of continued tapping even at daily intervals. Table XI shows the yields of dry rubber from 70 trees tapped at Henaratgoda. beginning in June 1908.

The trees were taken in groups of ten, numbered from I to VII respectively, and the average interval in days between successive tappings in the case of each group was as follows:

Table X. Average Intervals Between Tappings

Group

I.

II.

III.

IV.

V.

VI.

VII.

Days

1.275

2.225

3.35

4.425

5.525

6.55

7.325

The interval aimed at was an even number of days in each case. The actual excess was due to the fact that it was not always found possible to tap on the appointed day.

The tappings at longer intervals extended of course over a longer period of time than those at shorter intervals, consequently the climatic conditions are not identical in the case of the results recorded in different columns of Table XI. Nevertheless it will be observed that the variations in yield throughout the whole experiment were comparatively small.

In other experiments a larger initial increase in yield was observed. In such cases the results resemble those of Parkin more closely. It must be remembered also that the method of tapping employed was entirely different from that of Parkin, who used an incision method pure and simple, and did not reopen the same wounds. The result of all such experiments may be summarised as follows. With any moderate method of tapping, carried out at nearly equal intervals, which may vary in length from 24 hours up to 10 days, the yield per tapping rises rapidly to a point at which it is subsequently maintained, subject to certain variations the nature of which will be considered later on.

Table XI. First 40 Tappings

Total Rubber from 10 Trees tapped at intervals of 17 Days (nominal). (Weights in grammes; circumference in inches.)

I.

11.

III.

IV.

V.

VI.

VII.

Total Circumference of each Ten Trees.

No. of Tapping

362

359

313

366

336

402

396

1

194

143

155

149

117

135

114

2

159

130

194

237

146

175

169

3

224

185

197

140

146

225

188

4

231

148

138

235

158

220

194

5

235

133

197

190

141

241

172

6

168

174

152

190

174

245

141

7

I94

184

189

150

190

182

142

8

202

170

183

143

155

183

126

9

197

160

169

156

152

209

166

10

167

110

177

139

161

187

150

11

174

159

161

151

166

194

160

12

I96

170

141

155

140

208

171

13

I96

140

151

150

163

223

219

14

202

144

151

171

181

203

110

15

179

188

158

134

149

243

169

16

144

133

150

179

185

167

153

17

145

153

137

147

169

209

192

18

156

140

153

196

177

188

186

19

87

133

136

134

176

291

154

20

1l6

103

158

202

170

237

184

21

129

123

154

180

177

208

l56

22

105

110

127

141

190

203

148

23

98

97

153

170

180

292

156

24

145

106

150

148

200

230

189

25

128

82

151

171

163

188

157

26

105

92

146

166

192

198

154

27

134

102

110

168

21l

205

160

28

133

112

180

151

186

197

155

29

133

111

66

167

165

208

141

30

126

98

211

148

159

181

133

31

114

67

159

152

138

148

154

32

98

86

140

159

163

190

143

33

102

59

137

181

207

160

128

34

94

98

139

157

174

115

35

120

109

131

148

161

130

113

36

92

132

147

120

158

158

98

37

80

113

90

141

158

141

130

38

85

105

152

160

184

139

92

39

104

118

153

l60

155

106

88

40

123

65

181

164

147

104

81

Total

5,914

4,885

6,124

6,494

6,707

7,725

5,953

Total divided by circumference

163

13.6

19.5

17.7

20.0

19.2

15.0

1 An interval of 11 days between the *8th and 19th tapping of row I., and between the 14th and 15th tapping of row II.