260 Crystals in Testa and Pericarp of several Orders of Plants, 



the plant. Many of the raphides and different forms are figured, 

 after my old and extensive researches, in ' Science Gossip ' for May, 

 1873. In the ' Quarterly Journal of Microscopical Science,' July, 

 1873, I have given an engraving of the crystals in the testa of the 

 elm ; and now is to be added a notice of similar crystals in the same 

 part or its covering of other plants. 



Hoiv to find the Crystals. — These crystals are most easily found 

 in the seed-coat or pericarp, while it is yet somewhat soft and trans- 

 parent before it acquires hardness and opacity by perfect ripeness. 

 The thinnest possible sections are to be placed in a drop of water 

 or glycerine on the object-plate, and firmly pressed down by the 

 glass cover. Thus they may be examined first with an objective 

 of half an inch focal length, and afterwards with deeper powers 

 from |th to xVith. This last will probably not work through glass 

 covers of common thinness, but it may act satisfactorily when the 

 focus is lengthened and the power increased by the immersion 

 front. Another and easier plan, often very successful and always 

 useful, is to mash up or comminute minute and thin fragments, 

 by the point of a penknife, in a drop of fluid on the object-plate, 

 by which means, and the aid of needles, some very suitable bits may 

 be so divided and flattened as to show the crystals admirably. 



Distribution and Size of the Crystals. — They occur regularly 

 and constantly in the testa or pericarp of many plants, as I have 

 witnessed, for example, in the orders Tiliaceae, Aceraceae (Acer 

 campestre and A. pseudo-platanus), Geraniacese (Pelargonium, 

 Qeranium phoeum, G. pyreniacum, G. dissedum, and G. Boherti- 

 anum), Grossulariacese {Ilibes grossularia and R. ruhrum), Primu- 

 lacese [Anagallis ftrvews^s), Ulmaceae ( Ulmus suherosa), T>ioacovea,cesQ 

 [Tamus communis), and some others. No doubt numerous additions 

 to this list will be made by future observers. But though in the 

 testa or pericarp of certain species of divers orders these crystals 

 are constantly present, they are as regularly absent from other 

 orders. Thus I have not yet found the like crystals in the testa of 

 Umbelliferae, Leguminosae, and many other sections of the British 

 flora ; and yet similar crystals abound in the pod and other parts 

 of leguminous plants. The crystals in the testa or ovary of Com- 

 positae I have figured in the number of ' Science Gossip' above cited. 



Though the crystals are often plainly seen, they are not always 

 easily found. In the horned poppy they are obscure and only about 

 ^^V(jth of an inch in diameter ; and in the maple and sycamore the 

 crystals often occur in isolated patches, or so scantily as to escape 

 notice. The crystals in the gooseberry and the elm are about ^oVo^h 

 of an inch in diameter, and so very distinctly and regularly studded, 

 each within a plain cell, throughout the testa as to present an 

 appearance of crystalline tissues, forming very pretty microscopic 

 spectacles ; while in the red currant the crystals are scarcely half 



