XVII C^SALPINIA 191 



failed to induce the germination of seeds which, after floating a 

 year in sea-water, were kept in moist soil at a high temperature. 

 In one case a temperature varying from 80° to 110° F. was sustained 

 for several weeks, and in the other experiment a temperature of 

 80° to 90° was kept up for five months. When, however, an incision 

 was made into the epidermis, or the seed-coats were partially 

 penetrated with a file, the seeds swelled up in a day or two, and in 

 a few days began to germinate. 



The rapid transformation of the stone-like seed into a softened, 

 swollen, germinating mass ranks amongst the numerous little 

 wonders of the plant world. The seed, in fact, assumes again the 

 appearance of immaturity, and in so doing it suggests to us that 

 the rest-stage exemplified in the hard, pebble-like seed is but an 

 adaptation to general climatic conditions, and that in a region of 

 great heat and humidity, where there are no seasons, and where the 

 sun's rays are for ever screened off by mist and cloud, it could be 

 dispensed with altogether. One of my Hawaiian dreams was to 

 establish vivipary in Caesalpinia bonducella by subjecting the 

 maturing pod on the plant to very warm and humid conditions, my 

 expectation being that the soft, swollen seed would at once proceed 

 to germinate in the pod, and that the final process of setting, as 

 indicated by the induration and contraction of the coats, or in 

 other words the rest-stage, would be done away with. The dream, 

 however, bore some fruits in enlarging my standpoint in the 

 matter of vivipary, and I have referred to the subject in Chapter 

 XXXI. 



The seed-shell, about i'5 mm. in thickness, consists of three 

 coats : the outer skin very tough and waterproof ; the inner skin 

 seemingly permeable ; and the intermediate layer of hard prismatic 

 tissue, the " prismenschicht " of Schimper (p. 164). This middle 

 layer absorbs water rapidly and in large quantity, so that if a 

 fragment of the shell is placed in water it will be found after a 

 day's soaking to be three times as thick as it was in the dry state. 

 If one files a seed, or makes a small incision, so as to expose the 

 middle layer without piercing the inner coat, and then places it in 

 water, it will be noticed that the middle layer at once begins to 

 absorb water ; and within a couple of days the whole seed will 

 swell and attain the size it possessed in the so-called immature 

 condition. During the process the outer skin stretches, usually 

 without rupturing ; and all three coats, previously so hard that a 

 heavy blow with a hammer is required to break the seed, become 

 in a day or two soft enough to be easily cut with a knife. The 



