24 GoRHAM, on the UmbelUfercs. 



the absence of this in a boy's kite, which has, so to speak, 

 only a marginal vein outside, and a midrib in the centre, is 

 the reason why it is so often torn into tatters. 



In the foregoing brief and very partial survey of the veins 

 in the Umbellifers, sufficient has been said, I trust, to make 

 that portion to which I was anxious to direct attention clear 

 and intelligible ; while it may serve to show, also, that the 

 distribution of the veins in leaves, in this as well as in many 

 other natural orders of plants, will bear revision, which, when 

 accomplished, will render the description more complete, and 

 so facilitate classification. It is clear that the examination of 

 the leaf in the way described in this paper is both interesting 

 and instructive. 



The truth is, that the different parts of a flowering 

 plant often require lenses of different powers to define them 

 clearly. It is then only that they become intelligible ; for, 

 as might naturally be expected, the more minute the object to 

 be examined, the higher the power necessary to present it, to 

 the eye. This is well exemplified in a fern leaf during its 

 fructification, although any other plant, having several organs, 

 all differing in size, would do as well. In the fern the thin 

 layer of cellular tissue (indusimri) which envelopes the fruit 

 is visible to the naked eye, but is seen to the best advantage 

 by using a low power of from ten to twelve diameters. 



Next in order come the capsules or sporangia (cases in which 

 the seeds are contained). These demand a power of about 

 from 80 to 100 diameters. Next the spores (seeds) themselves, 

 which cannot be well defined under a power of less than 200 

 or 300 diameters. Besides these fructifying organs there are 

 the veins in the leaves, which can generally be seen under 

 about 12 diameters. In this way, and this only, by careful 

 adjustment of the power to the size of the object, can the 

 parts of a plant be presented to the eye intelligibly. For 

 suppose the order of arrangement to be reversed — a strong 

 power for an object of larger size, and a weak power for one 

 of smaller dimensions — all would be confused and indefinite. 

 The spores themselves would be seen only as amorphous 

 specks of matter under a weak lens ; and the indusia, under a 

 strong lens, too little of their area being thus exposed to 

 render their shape visible, Avould be reduced to a mere aggre- 

 gation of dots of cellular membrane. The bursting of the 

 sporangia, too, with the scattering of its spores, is a sight 

 worth seeing under a weak power, the spores shooting in all 

 directions across the field of view. This is well shown in a 

 recently gathered frond of Scolopendrium, the transit of the 

 spores reminding one of the saltatory movements observable 



