480 SU.MMAUY OF TURREXT RESEARCHES RELATING TO 



Anatomical Structure of the Stem of Compositae.* -M. P. Vuil- 

 lomin ilisc'usscs tliis subject from a systematic poiut of viow. He 

 regards tlic root, equally with tlic leaves, as au appendicular organ 

 attached to the stem ; and the various component parts of the stem he 

 classifies under the following heads : — E])idermi8 ; cortex, composed 

 of exoderm, endodcrra, and autoderm ; and central cylinder, composed 

 of pericycle and autocycle. The function of tlje endoderm is, according 

 to tlie author, not so much a protecting or isolating ono which has 

 acquired for it the term " gaiue protectrice," as to furnish resistance 

 to the expansion of the central cylinder, not being developed when 

 the endoderm has become transformed into a hardened ring, but only 

 when it is the seat of active cell-division, C8j)ecially when it gives rise 

 to adventitious roots. 



Tlie course of the fibrovascular bundles in the stem of Compositro 

 is arranged under five types ; while the mode of insertion of the buds 

 in the stem is referable to a single type only, the special variations 

 of wliich furnish a good anatomical character for indicating the 

 alliance of species. 



The development of the roots always takes place at the expense of 

 the jiericycle, both in the stem and in the root. 



There is not, in the Compositae, the same relationship between the 

 anatomical structure of the stem and the floral characters as occurs in 

 the Umbelliferaj. 



Structure of the Stem of Aquatic Plants.f — M. J. Costantin has 

 performed a series of experiments for the purpose of proving how far 

 the placing of a stem in water, air, or soil, modifies its structure ; and 

 for this purpose he placed different parts of the same axis in the three 

 media. He finds, on a comparison of the aquatic and aerial regions, 

 that in the former the air-passages are more developed^the vascular 

 system is reduced, and the vessels enlarged ; the fibrous tissue and 

 the collenchyma diminish in importance, but persist for a long period 

 in a degraded state ; while the endodermic punctations are very 

 visible, even when wanting in the aerial stem. A comparison of 

 aquatic with underground stems shows that in the latter the air- 

 passages are smaller ; the vascular system is somewhat less developed ; 

 the fibres and the collenchyma disappear almost entirely ; the peri- 

 pheral layers become suberized ; and the endoderm is more ditferen- 

 tiated. Of the three regions, therefore, the aquatic displays the least 

 development of the vascular system ; while tUe supporting structure 

 is more pronounced. 



Amphibious plants partially preserve this aerial structure in the 

 aquatic region, when their lower part only is immersed in water ; but, 

 when growing in deeji water, the organisation becomes completely 

 degraded. Aquatic plants do not therefore change their structure so 

 completely as terrestrial plants ; while transitiimal states, which are 

 almost entirely wanting in the latter, are much more numerous in the 

 former. 



* Viiilleniin, P., ' De la valeur des caiacteTes anatnnii.^uos nu point de vuo 

 de la cla-sififation des ve'ge'taiix,' 2.^^ i>p. and 47 fijjs., 8vo, rari.-i, 1884. 

 t Ann. Sci. Nat.— Bot.. xix. (l8S4j j.p. '2S7-:^;il (4 pis.). 



