PAMMEL ON THE SEED-COATS OF EUPHORBIA. 549 



Collomia linearis. — "The genus Collomia, like several other genera 

 oi PolemoniacecB, is remarkable for a mucous matter in which the seeds 

 are enveloped : if the seeds are thrown into water, this mucus instantly 

 dilates and forms around them like a cloud, and in a short time acquires a 

 volume greater than that of the seed itself. Upon examining the cause of 

 this singular phenomenon, it will be found to depend upon the presence 

 of an infinite multitude of exceedingly delicate and minute spiral vessels, 

 lying coiled up, spire within spire, on the outride of the testa; when dry, 

 these vessels are confined upon the surface of the seed by its mucus, with- 

 out being able to manifest themselves ; but the instant water is applied the 

 mucus dissolves, and ceases to counteract the elasticity of the spiral ves- 

 sels, which then dart forward at right-angles with the testa, each carry- 

 ing with it a sheath of mucus, in which it for a long time remains en- 

 veloped, as if in a membranous case. This observation is particularly 

 interesting, inasmuch as spiral vessels are, we believe, now for the first 

 time seen upon the external surface of a vegetable organ; they have been 

 hitherto supposed to exist solely within the substance of plants, accom- 

 panying either the medullary sheath, or the veins which diverge from it — 

 with one or two exceptions, of which the seeds of Casuarina is one." 



Lindley^^ further says about Collomia heterophylla : 



"It offers what seems to be an explanation of the nature of the sup- 

 posed spiral vessels in the testa of C linearis. Its testa is in like manner 

 mucilaginous, and, if examined with a'.high magnifier, is seen to be cov- 

 ered with an entangled mass of hairs, held together by the mucilage, 

 and evidently analogous to the coma of some plants, but most particu- 

 larly to those hairs that cover the surface of certain of the Convolvulus 

 tribe, to which Polemoniacece have a strong affinity." 



Mr. Richard Kippist^^ in an excellent paper has called atten- 

 tion to the presence of spiral cells in the seeds of some of the 

 A.ca)ithacC(X. In Acaiithodiiini spicatnm it is thus described : 



The seed " is of lenticular form, covered, especially towards the mar- 

 gin, with whitish hairs, which are closely appressed to the surface, and 

 glued together at their extremities, so as rather to resemble corrugations 

 of the testa than distinct hairs; on being placed in water, however, they 

 are set at liberty, and, expanding on all sides, are seen to consist of fasci- 

 cles of long, cylindrical, transparent tubes, firmly cohering for about 



Behrens : The Microscope in Botany. English translation by N. B. Hervey, Bos- 

 ton, iSSs, p. 327-367. This work contains an excellent bibliography. 

 27. Miscellaneous Works, vol. i. No. 549. 

 2S. Edwards' Botanical Register, vol. xiv. (1S2S) , No. 1166. 



29. Edwards' Botanical Register, vol. xvi. (1830), No. 1347. 



30. "On the existence of Spiral Cells in the Seeds of Acanthacere." Transactions of 

 the Linna;an Soc, vol. xix., p. 65. Read March 17, 1S4C. 



