116 SELECTED NOTES. 



with a Lieberkuhn. It is only when thus seen that the beautiful 

 pavement at the bottom of each well is effectively shown. 



A. Nicholson. 



Parasites to Mount— I first soak them in glycerine and water, 

 then place them on a slide, add warm jelly, put on cover, and 

 keep the jelly liquid for some time. To show the ramifications of 

 the minute tracheae, mounting in warm jelly without previous 

 soaking, and allowing them to cool rapidly, answers well. 



D. Moore. 



Spiral Fibre in Rhubarb.— This is a favourable opportunity to 

 draw the attention of members to a theory of their formation, 

 which was taught by Dr. Bristowe when I was student, and which 

 he elucidated in a paper in the St. Thomas's Hospital Reports a 

 few years ago. He supposes that the spiral dotted and pitted 

 appearance in cells is produced by the mechanical action of 

 growth acting on a sclerogenous layer (deposited in their interior) 

 when in a viscid state. He illustrates it by reference to the 

 parallelogram of forces. Thus the viscid layer of sclerogen is 

 stretched by the enlargement of the cell-wall in various degrees in 

 two or more directions, the result being a tendency to tear in a 

 direction representing the resultant of such forces. 



I went into the subject some time ago, and came to the con- 

 clusion that the theory was probably right. A good illustration I 

 found in the common garden clematis. In a terminal joint where 

 there is a most rapid growth, and the forces of growth act most 

 evenly, spirals only are found in a second joint. All stages of the 

 tearing process may easily be observed in the newly-formed scle- 

 rogenous layer ; the original spirals formed when the now second 

 joint was the first, are only stretched open somewhat or increased 

 in size. He thus suggests that they are not deposited as spirals, 

 but as an homogeneous layer of sclerogen, which is made into a 

 spiral or other form by the enlargement and lengthening of the 

 cell-wall by the action of growth, the form being determined by 

 surrounding conditions influencing the amount of stretching force 

 exerted in various directions. 



Spiral vessels are common in all quickly-growing portions of 

 plants, and this theory connects together the more rapid growth in 

 such parts with the presence of spiral fibres in certain cells, and is, 

 1 think, worth a hearing and further investigations. It is possible 

 that the same theory may account for the formation of the spiral 

 in the trachese of insects, but as yet known facts are too few to 

 admit of anything but conjecture. D. Moore. 



[The above note should have appeared in our January issue, 

 but was pressed out. — Editor?^ 



