SECT. i. LATICIFEROVS VESSELS. 177 



they are thin branching flexuous tubes, meandering 

 through the passages or interstices of the cellular tissue, 

 and occasionally filling the lacunae. 3 



Every one of the preceding tissues may be found in 

 many of the highest class of vegetables those which 

 are distinguished by having seeds with two lobes or seed 

 leaves, such as our common trees, shrubs, and most of 

 the herbaceous plants. Palms, the cereals, grasses, canes, 

 and all plants having seeds with but one lobe, which 

 form the second class, consist of cellular tissue mixed 

 with fibro-vascular bundles ; whilst in the third or flower- 

 less spore-bearing class, there is a general tendency 

 to a more and more simple structure, from the tree fern 

 to the lichens and algae, which last consist of cellular 

 tissue alone, and contain the lowest germs of vegetable 

 life. 



In seeds the miniature plant is enclosed between the 

 two lobes, as in peas and beans, or in a cavity of a lobe, 

 as in a grain of wheat or barley ; and all the parts of 

 the embryo are merely developed into the perfect plant 

 during the progress of vegetation. A spore, on the 

 contrary, which is the seed of a Cryptogam, or flower- 

 less class of plants, is a most minute globular cell, 

 full of granular matter, in which no embryo has yet 

 been discovered, so that the parts of the future plant 

 are supposed to be formed during the progress of vege- 

 tation, instead of being developed. Seeds, and spores 

 also, sometimes produce new varieties, while buds and 

 offsets only transmit the parent plant, with all its 

 peculiarities. In the higher classes, the organs of 

 nutrition and reproduction are always separate ; in the 

 lowest grades of vegetable life they are often the same. 

 Seeds bear no proportion to spores either in size or num- 



* 'Remarks on the Vessels of the Latex, the' Vasa Propria, and the 

 Receptacles of the elaborated Juices of Plants.' By M. Lestiboudois, 

 1 Comptes rendus,' 1863. 



VOL. i. y 



