1881.] 



MICROSCOPICAL JOURNAL. 



165 



These fibres now and then overlap 

 each other, and form a continuous 

 line the whole length of the slide ; or, 

 in other words, a dotted vessel. In 

 the same slide the vascular system, 

 properly so called, is only represent- 

 ed by a single annular duct. 



The cause of some of the structures 

 in the leaf and petiole oiNuphar, as- 

 suming the stellate form, may per- 

 haps be found in the circumstance, 

 that in the loose tissue of the leaf, 

 the vascular system is hindered in its 

 linear development because deprived 

 at intervals of a proper support ; and 

 in search of support it gropes its way 

 from a common base in many direc- 

 tions, assuming thus the stellate form. 

 In the petiole the vascular fibres find 

 the necessary support which enables 

 them to follow a straight line. The 

 branches of the " stars " may also 

 help to keep apart the air-chambers 

 of the leaf, otherwise the loose cellu- 

 lar tissue would collapse. 



Remarks on the Preceding 



Article on ** Internal 



Hairs." 



BY CHAS. F. COX, F.R.M.S, 



I thank you tor your courtesy in 

 allowing me to see Mr. Krutt- 

 schnitt's communication ; but I do 

 not feel that he and I are so seriously 

 at variance in our views that I need 

 to enter into extended discussion of 

 them at present. One thing, however, 

 seems to me beyond doubt, that in 

 the leaf of Nymphcea or Nuphar the 

 principal part of the " internal hairs " 

 are planted in the uppermost paren- 

 chymal (or the only truly epidermal) 

 layer, as may be seen in any good 

 transverse section of the leaf, made 

 at right angles to the mid-rib. In this 

 respect, at least, they stand in a very 

 evident relation to the epidermis. 

 But there are also numerous hairs 

 scattered through the lower paren- 

 chymal layers, projecting through 

 the tissue into the intercellular spaces, 

 and these, I imagine, are the continu- 

 ation into the leaf of the system of 



'* stars " which Mr. Kruttschnitt 

 speaks of as studding the large canals 

 in the petiole. The fact that these 

 " stars " take, by preference, to the 

 walls of the canals, is one indication 

 of their similarity in habit to all ex- 

 ternal hairs. Perhaps at some future 

 time I will undertake to present a 

 theory of the variations in form and 

 distribution of these internal hairs. 



I have long been familiar with the 

 elongated forms found in the petiole, 

 but I cannot see their equivalence to 

 a vascular system. The elongation I 

 take to be a change of form occa- 

 sioned by the rapid onward sweep of 

 growth in the petiole, confined within 

 narrow limits laterally ; the " star " 

 shape being the normal one of which 

 this is a modification. The fact that the 

 elongated hairs overlap one another 

 occasionally, does not seem to me to 

 indicate any real similarity to a vas- 

 cular system, so long as there is no 

 actual communication or connection 

 between them ; and the term, " a 

 dotted vessel," strikes me as decep- 

 tive, since the dotting referred to is 

 caused merely by the siliceous gran- 

 ules, which are common on all hairs. 

 Finally, I cannot see that the branch- 

 ing of the " stars " is accounted for on 

 the ground of necessity, since many 

 other water-plants have a cellular 

 structure quite as loose as that of Nu- 

 phar or NymphiBa, without possessing 

 the "stars," to prevent its collapse; and 

 the modification of a vascular system 

 into disconnected, stellately-branch- 

 ing bodies for this purpose would 

 seem to mean inconsistency of nature. 



And now that I am writing, 

 let me call attention to another 

 branch of this general subject. In my 

 paper on " the Epidermal Organs of 

 Plants," I stated that no one, as far 

 as I was then aware, had attempted 

 to account for the existence of hairs 

 on purely physiological grounds. 

 Since the publication of my article I 

 have seen, for the first time. Prof. J. C. 

 Arthur's paper on "Various Forms 

 of Trichomes of Echinocystis lo- 

 bata," which was published in the 



