ORIGIN OF STARCH LEUCOPLASTS. 



59 



grains are produced by leucoplasts, but such leucoplasts are not 



usually easy to see. About the most favourable material, if it 



can be obtained, is the comparatively young pseudo-bulb of one 



of the tropical orchids very widely cultivated in glass-houses 



for decorative purposes, viz., Phajus grandifolius. We halve 



a pseudo-bulb, make thin longitudinal radial sections from its 



apical pprtion, and rapidly transfer for examination to normal 



iodine solution diluted with half its volume of distilled water. If 



we turn our attention to the deeper portions, which have not 



been injured in cutting, we shall find without difficulty, at the 



base of the large and very eccentric 



starch grains, the flat elliptically elon- 



gated colourless leucoplasts (Fig. 21 



B], appearing rod-like in profile (Fig. 



21 A). Each leucoplast encloses a 



rod-like protein crystal, or crystal- 



loid. Towards the surface of the 



green pseudo-bulb the leucoplasts 



begin to be coloured green, and take 



gradually the colour and ordinary 



appearance of chlorophyll bodies. 



This material can be cut up small 



and fixed in concentrated picric acid 



for about twelve hours, carefully 



J FIG. 21. Leucoplasts ot Phajus 



washed in water to remove all the grandtfclius, from the pseudo-bulb. 

 acid, and preserved in alcohol. from above^e and />! with thl starch 



Leucoplasts in Iris. A moder- grains still quite small ; ^, coloured 

 . i r ui V j i. green (xo40). 



ately favourable object, and one not 



difficult to obtain, is furnished by the rhizome of Iris germanica. 



Surface-sections of this are made parallel with the surface of the 



rhizome. The outermost layer of tissue is 



rejected, and to this follow the starch layers. 



The observation is in this case best made in 



water. In uninjured cells the leucoplasts 



appear as aggregations of protoplasm at the 



hinder end of the starch grain (Fig. 22). These 



latter increase only at this end, and have a 



, . i-, . . mi i ers with starch grains 



proportionally eccentric structure. The leuco- from tll r i lizome O f iris 





FIG. 22. Starch form- 



plasts while under observation rapidly become </> ( x 540). 

 granular, and separate at length into smaller grains, which show 

 molecular movement " Brownian movement". Two starch 



